Ecophenotypic Plasticity Research Articles

Adaptive shell-morphological differences and differential fitness in two morphospecies of Lanistes (Gastropoda: Ampullariidae) from the northern region of the Malawi Basin

Abstract Environment–phenotype correlations are a central pattern of adaptive radiations, but such correlations and the expected associated reciprocal differences in fitness of divergent phenotypes in their respective niches are rarely demonstrated. Ecophenotypic plasticity may result in environment–phenotype correlations too, however, so that certain observed morphological differences, even in adaptive radiations, may result from plasticity instead of differential adaptation. Here, we examine the nature of observed morphological differences in two morphospecies of Lanistes gastropods from the northern region of the Malawi Basin that are part of an ongoing adaptive radiation. We subjected experimental populations of each of these two morphospecies, i.e. L. sp. (solidus-like), which occupies intralacustrine habitats with comparatively stable environmental conditions, and L. sp. (ovum-like), which occurs in satellite waterbodies with fluctuating environmental conditions, to a common garden experiment in the laboratory. Our experimental conditions approximated those of stable, intralacustrine habitats. We monitored fecundity and subjected wild-caught parents and intraspecific F1 offspring to semilandmark geometric morphometrics. L. sp. (solidus-like) exhibited higher fecundity than L. sp. (ovum-like). Whereas wild-caught parents of both morphospecies had similar shell sizes, 9-month-old F1 offspring of L. sp. (solidus-like) were significantly smaller than those of L. sp. (ovum-like), indicating slower growth. Substantial shell-morphological differences were observed between the two morphospecies in the wild-caught parents as well as in F1 offspring, indicating that shell-morphological differences are genetically inherited. Our results also indicate differential fitness but fully reciprocal transplant experiments would be required to demonstrate local adaptation.

Ecophenotypic variation or genetic differentiation? Ambiguity of morphological and molecular relationships presents uncertainty in host-specific plasticity of Chelonibia barnacles

The genus Chelonibia, informally referred to as the turtle barnacles, was historically subdivided into four species by both morphological differentiation and host affinity. More recent studies, however, hypothesized that three of these barnacle species – C. testudinaria, C. manati, and C. patula – comprise a single species, C. testudinaria, that exhibits host-specific ecophenotypic plasticity. In this study, we examined both morphological and molecular datasets to assess whether host attachment or genetic differentiation best explains the morphotypes assigned to C. testudinaria and C. manati. For morphology, we compared 11 mensural test and cirral characters from 71 C. testudinaria and 25 C. manati specimens identified by the previously established absence or presence of a ridged external dorsal surface. The two morphotypes overlapped in overall body size, although C. testudinaria averaged significantly larger and C. manati exhibited relatively longer cirri. Discriminant function analyses (DFA) showed strong but incomplete differentiation (92.6% classification success), with one C. manati morphotype collected from a sea turtle classified with high confidence as C. manati. Thus, the morphological data contradict the host-specificity hypothesis. Genetic analyses using three target loci (16s, 28s, COI) from the mitochondrial and nuclear genomes, as well as a single concatenated sequence of >1600 bp, likewise failed to support genetic differentiation between the two morphotypes within the Atlantic sample. With inclusion of a broader sample of Atlantic C. testudinaria and C. manati and Pacific C. testudinaria barnacles, we found strong population distinction between the ocean basins without morphotype separation. Results of the present study suggest that Balanomorph barnacle taxonomy, especially of endosymbiont species, requires further study, as neither phenotypic plasticity nor genetic differentiation accounted for existence of the two distinct morphotypes.

Exploring the phylogenetic signal in the cranial variation of European populations of grayling (Actinopterygii, Salmonidae)

Abstract This is a preliminary and exploratory study of cranial variation in European populations of grayling. We investigated the correspondence between size/shape variation of the dorsal (dc), ventral (vc) and occipital (oc) cranium and phylogenetic relationships (inferred from mitochondrial control region – mtDNA cr and microsatellite dna data) of six grayling populations: three from Balkan phylogenetic clade and two from Caspian phylogenetic clade of the European grayling Thymallus thymallus and one population of the Adriatic grayling Thymallus aeliani, which until recently was considered the Adriatic phylogenetic clade of T. thymallus. Significant size and shape differences were found between populations in all three cranial views. However, significant size-related shape variation (allometry) was found for dc and vc, but not for oc. The size variation of each cranial view does not contain phylogenetic signal, but size variation of oc is consistent with genetic variation inferred from microsatellite dna. Regarding shape variation, a significant phylogenetic signal was detected only for oc, and only the shape variation of oc is consistent with the genetic variation inferred from the mtDNA cr. Moreover, the Adriatic grayling T. aeliani (Soča population) was clearly separated from the three T. thymallus populations of the Balkan phylogenetic clade and the two T. thymallus populations of the Caspian phylogenetic clade only at the level of oc. Thus, our results suggest that different cranial regions differ in allometry, reflect phylo(genetic) relationships differently, and exhibit differences in ecophenotypic plasticity, with oc seeming best suited to represent the phylogenetic relationships of the grayling populations studied.

Geographic and temporal morphological stasis in the latest Cretaceous ammonoid Discoscaphites iris from the U.S. Gulf and Atlantic Coastal Plains

AbstractWe examine temporal and spatial variation in morphology of the ammonoid cephalopod Discoscaphites iris using a large dataset from multiple localities in the Late Cretaceous (Maastrichtian) of the U.S. Gulf and Atlantic Coastal Plains, spanning a distance of 2000 km along the paleoshoreline. Our results suggest that the fossil record of D. iris is consistent with no within-species net accumulation of phyletic evolutionary change across morphological traits or the lifetime of this species. Correlations between some traits and paleoenvironmental conditions as well as changes in the coefficient of variation may support limited population-scale ecophenotypic plasticity; however, where stratigraphic data are available, no directional changes in morphology occur before the Cretaceous/Paleogene (K/Pg) boundary. This is consistent with models of “dynamic” evolutionary stasis. Combined with knowledge of life-history traits and paleoecology of scaphitid ammonoids, specifically a short planktonic phase after hatching followed by transition to a nektobenthic adult stage, these data suggest that scaphitids had significant potential for rapid morphological change in conjunction with limited dispersal capacity. It is therefore likely that evolutionary mode in the Scaphitidae (and potentially across the broader ammonoid clade) follows a model of cladogenesis wherein a dynamic morphological stasis is periodically interrupted by more substantial evolutionary change at speciation events. Finally, the lack of temporal changes in our data suggest that global environmental changes had a limited effect on the morphology of ammonoid faunas during the latest Cretaceous.

Ecophenotypic plasticity in shell growth direction of asari clamRuditapes philippinarum

AbstractAsari clam (or Manila clam)Ruditapes philippinarumis an important bivalve for local fisheries. This species exhibits a large variation in shell morphology, and the shell roundness tends to be greater in more unsuitable habitats. To test whether the increments in shell size parameters (length, height and width) were affected solely by environmental conditions or by internal factors such as initial shell shapes or growth rate, a field caging experiment was conducted at two different sites of unsuitable and suitable habitats in Matsukawaura Lagoon, Japan, where shell shapes of wild clams were significantly different between the habitats. In the experiment, clams were released from the two sites to the same site or to the other site and were re-collected after 3, 6 and 12 months of caging. Caged clams originating from unsuitable habitats and released to suitable habitats showed a reduction in shell height relative to shell length, while clams from suitable habitats introduced to unsuitable habitats showed marked increases in both shell height and width. Generalized linear mixed models suggested that the increase in shell height was affected largely by the release habitat (environment) whereas the increase in shell width was affected largely by the individual growth rate. These results suggest that marginal growths in shell height and width respond differently to external and internal factors of clams, resulting in plasticity in their shell shapes according to the environments to which they are translocated.

First report of extraordinary corkscrew gastropods of the genus Bulinus in Lake Malawi

Open-coiled shells are rarely observed in gastropods, but they may occur at a relative frequency ranging from a small percentage of specimens in a population up to being specific to populations or even species. The origin of such corkscrew-like shells are poorly understood, but may include developmental anomalies, ecophenotypic plasticity or genetic inheritance. Here, we report the first case of gastropods from Lake Malawi with corkscrew-like shells, and we use comparative molecular studies with two mitochondrial gene fragments (COI and 16S rRNA) to examine its origin. The specimens belong to the genus Bulinus, more specifically to one of five clades of Bulinus recovered from the Malawi Basin. Beyond being seemingly specific to one of these Bulinus clades, network analyses indicate low genetic differentiation from the other, regularly shaped specimens in this clade. Although our results do not fully discard the possibility of corkscrew-like shells being genetically inherited or being caused by growth disturbance, their restrictive occurrence in a few geographically isolated populations in sympatry with specimens displaying a regular shell shape supports the hypothesis that the corkscrew-like shell shape in Bulinus is caused by ecophenotypic plasticity. For now, it is unclear whether aspects of the physical environment, or biotic interactions, such as a release from predation, caused the corkscrew-like morphotype. The phenomenon may have been caused by the multiple environmental changes that Lake Malawi has been undergoing over recent decades.

The Canary in the Coal Mine: Testate Amoebae Record Anthropogenic Impacts in Sediments of Oligotrophic Lake George, NY, USA

ABSTRACT Lake George (NY) is surrounded by Forever Wild Forest in the Adirondack Park and has a Class AA Special water quality rating, yet lake monitoring has revealed increasing anthropogenic impacts from salt and nutrient loading over the past 30 years. To reconstruct anthropogenic influence on the lake (e.g., salt loading, eutrophication, climate warming), we characterized modern stable isotopes and testate amoeba and diatom assemblages in surface sediments from 33 lake-wide sites and compared their variability to 36 years of water-quality data. Linear regression analyses support testate amoebae as rapid responders and recorders of environmental change because taxa are strongly correlated with percent change of important water quality parameters. Our assessment indicates that: 1) Netzelia gramen is associated with aquatic plants and filamentous algae, making them a valuable aquatic plant/alga indicator, which is supported by the co-occurrence of the diatom Cocconeis spp.; 2) difflugids are generally good indicators of eutrophication, except for Difflugia protaeiformis; and 3) seasonal differences in water quality trends are reflected in the fossil record on decadal time scales. We show that testate amoebae are highly sensitive to small environmental changes in an oligotrophic lake and exhibit established relationships from eutrophic and mesotrophic lakes as well as new, likely oligotrophic-specific correlations. Correlation coefficients of water quality variables and strains within a species also illustrate gradational relationships, suggesting testate amoebae exhibit ecophenotypic plasticity. Diatom and testate amoeba assemblages categorize modern lakebed sites into four subgroups: 1) benthic macrophyte; 2) high nutrient; 3) high alkalinity; and 4) salt loading assemblages.

Adaptive divergence in shell morphology in an ongoing gastropod radiation from Lake Malawi

BackgroundEcological speciation is a prominent mechanism of diversification but in many evolutionary radiations, particularly in invertebrates, it remains unclear whether supposedly critical ecological traits drove or facilitated diversification. As a result, we lack accurate knowledge on the drivers of diversification for most evolutionary radiations along the tree of life. Freshwater mollusks present an enigmatic example: Putatively adaptive radiations are being described in various families, typically from long-lived lakes, whereas other taxa represent celebrated model systems in the study of ecophenotypic plasticity. Here we examine determinants of shell-shape variation in three nominal species of an ongoing ampullariid radiation in the Malawi Basin (Lanistes nyassanus, L. solidus and Lanistes sp. (ovum-like)) with a common garden experiment and semi-landmark morphometrics.ResultsWe found significant differences in survival and fecundity among these species in contrasting habitats. Morphological differences observed in the wild persisted in our experiments for L. nyassanus versus L. solidus and L. sp. (ovum-like), but differences between L. solidus and L. sp. (ovum-like) disappeared and re-emerged in the F1 and F2 generations, respectively. These results indicate that plasticity occurred, but that it is not solely responsible for the observed differences. Our experiments provide the first unambiguous evidence for genetic divergence in shell morphology in an ongoing freshwater gastropod radiation in association with marked fitness differences among species under controlled habitat conditions.ConclusionsOur results indicate that differences in shell morphology among Lanistes species occupying different habitats have an adaptive value. These results also facilitate an accurate reinterpretation of morphological variation in fossil Lanistes radiations, and thus macroevolutionary dynamics. Finally, our work testifies that the shells of freshwater gastropods may retain signatures of adaptation at low taxonomic levels, beyond representing an evolutionary novelty responsible for much of the diversity and disparity in mollusks altogether.

Riverscape genetic variation, migration patterns, and morphological variation of the threatened Round Rocksnail, Leptoxis ampla.

Within riverine systems, headwater populations are hypothesized to harbour higher amounts of genetic distinctiveness than populations in the main stem of a river and display increased genetic diversity in large, downstream habitats. However, these hypotheses were mostly developed with insects and fish, and they have not been tested on many invertebrate lineages. Pleuroceridae gastropods are of particular ecological importance to rivers of eastern North America, sometimes comprising over 90% of macroinvertebrate biomass. Yet, virtually nothing is known of pleurocerid landscape genetics, including whether genetic diversity follows predictions made by hypotheses developed on more mobile species. Moreover, the commonly repeated hypothesis that intraspecific morphological variation in gastropods results from ecophenotypic plasticity has not been well tested on pleurocerids. Using 2bRAD-seq to discover single nucleotide polymorphisms, we show that the threatened, Cahaba River endemic pleurocerid, Leptoxis ampla, has limited gene flow among populations and that migration is downstream-biased, conflicting with previous hypotheses. Both tributary and main stem populations harbour unique genomic profiles, and genetic diversity was highest in downstream populations. Furthermore, L.ampla shell morphology was more correlated with genetic differences among individuals and populations than habitat characteristics. We anticipate similar genetic and demographic patterns to be seen in other pleurocerids, and hypotheses about gene flow and population demographics that were based on more mobile taxa often, but not always, apply to freshwater gastropods. From a conservation standpoint, genetic structure of L.ampla populations suggests distinctive genetic diversity is lost with localized extirpation, a phenomenon common across the range of Pleuroceridae.

The alien slipper limpet Crepipatella dilatata (Lamarck, 1819) in northern Spain: A multidisciplinary approach to its taxonomic identification and invasive biology.

The slipper limpet Crepipatella dilatata, native to Chile and Argentina, was introduced in Spain in 2005. The species was thought to inhabit the region of Rias Bajas, yet recently, putative C. dilatata populations have been documented on the coast of north-central Spain and in the Ebro Delta of the Spanish Mediterranean. Here we undertook a multidisciplinary approach to study the invasion biology of this species. Specifically, two geographically distant populations, one being a successfully established population from O Grove and the other a declining population from Gijon, were studied over the course of four years. Analyses of morphological and developmental traits as well as genetic information confirmed the presence of C. dilatata in these sites. The results revealed polymorphism in anatomical traits and shell shape. Shell shape polymorphism was unevenly distributed among sites and among sexes. Males were monomorphic, while females were polymorphic. Of the female morphotypes encountered, one was absent in the declining population from Gijón. Size at first female maturation and female size were greater in the declining population than in the established population. Reproductive success varied seasonally but not spatially among populations. In the established population, gregariousness was significantly greater; the size when sex changes was found to be plastic and socially controlled. The sex ratio of the declining population was female biased while in the established population the sex ratio changed during the study period from being balanced to being female biased. This change in sex ratio was probably due to higher male mortality. Molecular analyses pointed to the localities of Corral Bay in southern Chile and Puerto Madryn in southern Argentina as potential population sources. The intercontinental import of fresh mussels cultivated in Chilean farms is a likely source of this mussel in Spain. Comparison with available data of native populations of C. dilatata strongly indicate that ecophenotypic plasticity, socially controlled sex change, high gregariousness, increased nurse egg supply to viable larvae during the encapsulated developmental period, later maturation and larger female sizes altogether enhance establishment success of this non-indigenous species. Human-mediated factors like the intraregional mussel trade and transplantation are also likely secondary dispersal mechanisms favouring the spread of this organism.

Local versus Generalized Phenotypes in Two Sympatric Aurelia Species: Understanding Jellyfish Ecology Using Genetics and Morphometrics.

For individuals living in environmentally heterogeneous environments, a key component for adaptation and persistence is the extent of phenotypic differentiation in response to local environmental conditions. In order to determine the extent of environmentally induced morphological variation in a natural population distributed along environmental gradients, it is necessary to account for potential genetic differences contributing to morphological differentiation. In this study, we set out to quantify geographic morphological variation in the moon jellyfish Aurelia exposed at the extremes of a latitudinal environmental gradient in the Gulf of Mexico (GoM). We used morphological data based on 28 characters, and genetic data taken from mitochondrial cytochrome oxidase I (COI) and nuclear internal transcribed spacer 1 (ITS-1). Molecular analyses revealed the presence of two genetically distinct species of Aurelia co-occurring in the GoM: Aurelia sp. 9 and Aurelia c.f. sp. 2, named for its divergence from (for COI) and similarity to (for ITS-1) Aurelia sp. 2 (Brazil). Neither species exhibited significant population genetic structure between the Northern and the Southeastern Gulf of Mexico; however, they differed greatly in the degree of geographic morphological variation. The morphology of Aurelia sp. 9 exhibited ecophenotypic plasticity and varied significantly between locations, while morphology of Aurelia c.f. sp. 2 was geographically invariant (i.e., canalized). The plastic, generalist medusae of Aurelia sp. 9 are likely able to produce environmentally-induced, “optimal” phenotypes that confer high relative fitness in different environments. In contrast, the non-plastic generalist individuals of Aurelia c.f. sp. 2 likely produce environmentally-independent phenotypes that provide the highest fitness across environments. These findings suggest the two Aurelia lineages co-occurring in the GoM were likely exposed to different past environmental conditions (i.e., different selective pressures) and evolved different strategies to cope with environmental variation. This study highlights the importance of using genetics and morphometric data to understand jellyfish ecology, evolution and systematics.

Ecophenotypic plasticity leads to extraordinary gastropod shells found on the "Roof of the World".

The often extraordinary shell forms and shapes of gastropods found in palaeolakes, such as the highly diverse Gyraulus fauna of the famous Steinheim Basin, have been puzzling evolutionary biologists for centuries, and there is an ongoing debate whether these aberrant shell forms are indicative of true species (or subspecies) or ecophenotypic morphs. Interestingly, one of the Steinheim Gyraulus morphs – a corkscrew-like open-coiled shell – has a recent analogue in the Lake Bangong drainage system on the western Tibetan Plateau. Therefore, a combination of morphological, molecular, palaeolimnological, and ecological analyses was used in this study to assess whether the extraordinary shell shape in Gyraulus sp. from this drainage system represents a (young) ecophenotypic phenomenon or if it has been genetically fixed over an extended period of time. Our morphological, ecological, and palaeolimnological data suggest that the corkscrew-like specimens remain restricted to a small pond near Lake Bangong with an elevated pH value and that the colonization may have occurred recently. The phylogenetic reconstruction based on two gene fragments shows that these nonplanispiral specimens cluster within the previous described Tibetan Plateau Gyraulus clade N2. A network analysis indicates that some haplotypes are even shared by planispiral and nonplanispiral specimens. Given the ephemerality of the phenomenon, the compact network patterns inferred, the likely young phylogenetic age of the aberrant Gyraulus shells studied, and the ecological peculiarities of the study site, we suggest that the evolution of the aberrant shell forms on the Tibetan Plateau could likely be considered as a rapid ecophenotypic response, possibly induced by ecological stress. This finding may thus have implications for the ongoing debate about the processes that have caused the extraordinary shell diversity in palaeolakes such as the Steinheim Basin.

Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata

BackgroundPhenotypic plasticity is termed ‘cryptic’ when it becomes so extreme as to prompt an (erroneous) hypothesis of speciation. Populations of pleurocerid snails nominally identified as Pleurocera (‘Goniobasis’ or ‘Elimia’) livescens are common elements of the macrobenthos in rivers and on lakeshores from Vermont through northern Ohio and northern Indiana to Wisconsin, USA. Small streams in southern Ohio, southern Indiana, and Kentucky are inhabited by Pleurocera semicarinata, and larger rivers by Lithasia obovata. The three nominal species differ only in qualitative aspects of shell morphology - P. semicarinata demonstrating a slender shell with a small body whorl, L. obovata a robust shell with a large body whorl, and P. livescens intermediate.ResultsHere I use allozyme electrophoresis to estimate genetic divergence over 11 enzyme loci among three populations of P. livescens, two populations of P. semicarinata, and one population of L. obovata sampled across 650 km of their combined range. With each of these six populations I sample a control population of Pleurocera canaliculata, demonstrating that the genetic divergence among the six known conspecific populations is comparable to that observed among the six study populations.ConclusionsThe specific nomina L. obovata and P. livescens would appear to be junior synonyms of P. semicarinata. The shell morphological differences by which these taxa have heretofore been distinguished would appear to result from ecophenotypic plasticity, driven perhaps by predation, substrate, or current.

Evolutionary origins and genetic variation of the Seychelles treefrog, Tachycnemis seychellensis (Duméril and Bibron, 1841) (Amphibia: Anura: Hyperoliidae)

The hyperoliid frog Tachycnemis seychellensis, the only species of its genus, is endemic to the four largest granitic islands of the Seychelles archipelago and is reliant on freshwater bodies for reproduction. Its presence in the Seychelles is thought to be the product of a transoceanic dispersal, diverging from the genus Heterixalus, its closest living relative (currently endemic to Madagascar), between approximately 10–35Ma. A previous study documented substantial intraspecific morphological variation among island populations and also among populations within the largest island (Mahé). To assess intraspecific genetic variation and to infer the closest living relative(s) of T. seychellensis, DNA sequence data were generated for three mitochondrial and four nuclear markers. These data support a sister-group relationship between T. seychellensis and Heterixalus, with the divergence between the two occurring between approximately 11–19Ma based on cytb p-distances. Low levels of genetic variation were found among major mitochondrial haplotype clades of T. seychellensis (maximum 0.7% p-distance concatenated mtDNA), and samples from each of the islands (except La Digue) comprised multiple mitochondrial haplotype clades. Two nuclear genes (rag1 and tyr) showed no variation, and the other two (rho and pomc) lacked any notable geographic structuring, counter to patterns observed within presumably more vagile Seychelles taxa such as lizards. The low levels of genetic variation and phylogeographic structure support an interpretation that there is a single but morphologically highly variable species of Seychelles treefrog. The contrasting genetic and morphological intraspecific variation may be attributable to relatively recent admixture during low sea-level stands, ecophenotypic plasticity, local adaptation to different environmental conditions, and/or current and previously small population sizes. Low genetic phylogeographic structure but substantial morphological variation is unusual within anurans.

Spatial distribution of the sibling species of Anopheles gambiae sensu lato (Diptera: Culicidae) and malaria prevalence in Bayelsa State, Nigeria

BackgroundMuch of the confusing ecophenotypic plasticity of Anopheles gambiae sensu lato is attributable to the differential biological traits of the sibling species, with their heterogeneous geographical distribution, behavioral dissimilarities and divergent population dynamics. These differences are critical to their roles in malaria transmission. Studies were, therefore, undertaken on the spatial distribution of these species and malaria prevalence rates in Bayelsa State, September, 2008-August 2010.MethodsMosquito sampling was in 7 towns/villages in 7 Local Government Areas (LGAs) in 3 eco-vegetational zones: Fresh Water Swamp Forest (FWSF): Sagbama, Yenagoa, Kolokuma-Opokuma LGAs; Brackish Water Swamp Forest (BWSF): Ogbia, Ekeremor, Southern Ijaw LGAs; Mangrove Water Forest (MWF): Nembe LGA. Adults were collected twice quarterly by the Pyrethrum Spray Catch (PSC) technique. Anopheles was separated morphologically and the sibling species PCR- identified. Simultaneously, malaria prevalence rates were calculated from data obtained by the examination of blood smears from consenting individuals at hospitals/clinics.ResultsAn. gambiae s.s. was dominant across the 3-eco-vegetational zones. Spatial distribution analyses by cell count and nearest neighbor techniques indicated a tendency to clustering of species. An. gambiae s.s. and An. arabiensis clustered in Ekeremor LGA while these 2 species and An. melas aggregated in Nembe. The gonotrophic (physiological) status examination revealed that 34.3, 23.5, 23.1 and 18.4% of the population were fed, unfed, gravid and half gravid respectively. The highest malaria prevalence rates were obtained at Kolokuma-Opokuma and Nembe LGAs. Variation in prevalence rates among LGAs was significant (t = 5.976, df = 6, p-value = 0.002, p < 0.05). The highest prevalence rate was in the age group, 30-39 yrs, while the lowest prevalence was in the 0-9 yrs group.ConclusionHigh malaria prevalence rates were associated with An. gambiae s.s. either in allopatry or sympatry across eco-vegetational zones. In areas where the sibling species clustered, they probably formed nidi for transmission. Socio-economic conditions might have contributed to reduced prevalence in Yenagoa, State Capital.

A geometric morphometric re-evaluation of the use of dental form to explore differences in horse (Equus caballus) populations and its potential zooarchaeological application

The domestication of the horse – specifically its use as a transport animal – had a unique impact on the evolution of human societies. Along with its influence on warfare, the horse transformed land transportation, radically altering the distance that humans could travel in a day, week, month or lifetime. Over the last century horse domestication has been investigated by zooarchaeologists using morphometric, morphological and (more recently) biomolecular approaches in attempts to identify distinct ‘domestic’ phenotypes in the fossil record. However, identification of domestic morphotypes have been complicated by the low variation in equid cranial morphology and apparent limited changes brought about through the domestication process compared with other domestic taxa. Furthermore, cranial morphology is too prone to ecophenotypic plasticity to provide relevant taxonomic markers. Even dental morphology (of primary importance for taxonomic investigation in the fossil record) has been dismissed as a useful marker for horse domestication, since variations in tooth size and enamel patterns are considered to be too greatly influenced by age and continuous tooth wear. The proof-of-concept study presented here re-evaluates the potential of cheek teeth shape to capture significant differences between horse populations. Using geometric morphometrics (GMM), we study the enamel-folding pattern of the upper P2 and M3, selected for their distinctive morphology amongst the cheek teeth. Curated specimens of known age and sex from two horse (Equus caballus) breeds – Icelandic and Thoroughbred – were used to investigate whether the effects of age (through occlusal wear), sexual dimorphism and allometry (size-related change in shape) should be regarded as confounding factors preventing any accurate discrimination between these two populations. The results show that a landmark based approach applied to the occlusal enamel folding of the P2 and M3 captures significant differences in size (centroïd) and shape between the horses breeds studied. Age-related factors, allometric scaling and sexual dimorphism are not confounding factors in their discrimination, encouraging the use of dental form in population-based research on ancient horse remains.

Phylogenetic and morphometric analyses reveal ecophenotypic plasticity in freshwater mussels Obovaria jacksoniana and Villosa arkansasensis (Bivalvia: Unionidae).

Freshwater mollusk shell morphology exhibits clinal variation along a stream continuum that has been termed the Law of Stream Distribution. We analyzed phylogenetic relationships and morphological similarity of two freshwater mussels (Bivalvia: Unionidae), Obovaria jacksoniana and Villosa arkansasensis, throughout their ranges. The objectives were to investigate phylogenetic structure and evolutionary divergence of O. jacksoniana and V. arkansasensis and morphological similarity between the two species. Our analyses were the first explicit tests of phenotypic plasticity in shell morphologies using a combination of genetics and morphometrics. We conducted phylogenetic analyses of mitochondrial DNA (1416 bp; two genes) and morphometric analyses for 135 individuals of O. jacksoniana and V. arkansasensis from 12 streams. We examined correlations among genetic, morphological, and spatial distances using Mantel tests. Molecular phylogenetic analyses revealed a monophyletic relationship between O. jacksoniana and V. arkansasensis. Within this O. jacksoniana/V. arkansasensis complex, five distinct clades corresponding to drainage patterns showed high genetic divergence. Morphometric analysis revealed relative differences in shell morphologies between the two currently recognized species. We conclude that morphological differences between the two species are caused by ecophenotypic plasticity. A series of Mantel tests showed regional and local genetic isolation by distance. We observed clear positive correlations between morphological and geographic distances within a single drainage. We did not observe correlations between genetic and morphological distances. Phylogenetic analyses suggest O. jacksoniana and V. arkansasensis are synonomous and most closely related to a clade composed of O. retusa, O. subrotunda, and O. unicolor. Therefore, the synonomous O. jacksoniana and V. arkansasensis should be recognized as Obovaria arkansasensis (Lea 1862) n. comb. Phylogenetic analyses also showed relative genetic isolation among drainages, suggesting no current gene flow. Further investigation of in-progress speciation and/or cryptic species within O. arkansasensis is warranted followed by appropriate revision of conservation management designations.In this study, we found Obovaria jacksoniana and Villosa arkansasensis are synonomous. We suggest that morphological differences between the two species are caused by ecophenotypic plasticity, where V. arkansasensis is the upstream morphotype and O. jacksoniana is the downstream morphotype of a single species.

Articulated endoskeletons of the Devonian disparid Storthingocrinus: implications for the revision of a misunderstood crinoid genus

The discovery of new specimens and restudy of known collections result in revision of the disparid crinoid genus Storthingocrinus, known from the Middle Devonian of Europe and Asia. High ecophenotypic plasticity of the common S. fritillus negates the validity of several former subspecies and demonstrates the general morphologic variability of the cup proportions. This requires the definition of interspecific distinguishing features based on the description of articulated crowns. Three new species are described (Storthingocrinus coronatus n. sp., S. ebbighauseni n. sp., and S. lobatus n. sp.). A neotype is proposed for the lost original of S. fritillus. The proposed interpretation of Storthingocrinus trifidus as a stemless and pelagic crinoid is rejected, and its subgeneric status is dissolved based on the first recovery of articulated crowns with attached stems. Because “Storthingocrinus sphaericus” from the Upper Devonian of Germany is excluded from Storthingocrinus, and “Storthingocrinus haugi” as well as “Storthingocrinus labiatus” from the Lower Devonian of Spain were listed in the Official Index of Rejected and Invalid Specific Names in Zoology by the International Commission on Zoological Nomenclature (ICZN), the stratigraphic range of the genus is restricted to the Middle Devonian. The genus populated the southeastern shelf realm of Laurussia within the Rheic Ocean about 31°S latitude (Germany, Czech Republic; Europe), and the Prototethys/Paleotethys Ocean about 27°S latitude (Burma; Asia). A monobathrid camerate species from the Middle Devonian of the Eifel Synclines, which was incorrectly assigned to Storthingocrinus decagonus, is redescribed as Bohnerticrinus nilsjungi n. gen. n. sp.

Evolutionary history of relict Congeria (Bivalvia: Dreissenidae): unearthing the subterranean biodiversity of the Dinaric Karst

BackgroundPatterns of biodiversity in the subterranean realm are typically different from those encountered on the Earth’s surface. The Dinaric karst of Croatia, Slovenia and Bosnia and Herzegovina is a global hotspot of subterranean biodiversity. How this was achieved and why this is so remain largely unresolved despite a long tradition of research. To obtain insights into the colonisation of the Dinaric Karst and the effects of the subterranean realm on its inhabitants, we studied the tertiary relict Congeria, a unique cave-dwelling bivalve (Dreissenidae), using a combination of biogeographical, molecular, morphological, and paleontological information.ResultsPhylogenetic and molecular clock analyses using both nuclear and mitochondrial markers have shown that the surviving Congeria lineage has actually split into three distinct species, i.e., C. kusceri, C. jalzici sp. nov. and C. mulaomerovici sp. nov., by vicariant processes in the late Miocene and Pliocene. Despite millions of years of independent evolution, analyses have demonstrated a great deal of shell similarity between modern Congeria species, although slight differences in hinge plate structure have enabled the description of the two new species. Ancestral plesiomorphic shell forms seem to have been conserved during the processes of cave colonisation and subsequent lineage isolation. In contrast, shell morphology is divergent within one of the lineages, probably due to microhabitat differences.ConclusionsFollowing the turbulent evolution of the Dreissenidae during the Tertiary and major radiations in Lake Pannon, species of Congeria went extinct. One lineage survived, however, by adopting a unique life history strategy that suited it to the underground environment. In light of our new data, an alternative scenario for its colonisation of the karst is proposed. The extant Congeria comprises three sister species that, to date, have only been found to live in 15 caves in the Dinaric karst. Inter-specific morphological stasis and intra-specific ecophenotypic plasticity of the congerid shell demonstrate the contrasting ways in which evolution in the underground environments shapes its inhabitants.

Host‐specific morphologies but no host races in the commensal bivalveNeaeromya rugifera

AbstractSpeciation by host shift is one of the explicit models of ecological speciation. A prerequisite of this model is the formation of host races (sympatric populations that show host‐specific genetic structuring and phenotypes). Many members of the diverse marine bivalve superfamilyGaleommatoidea have obligate commensal relationships with invertebrate hosts. Some species have the ability to occupy multiple host species, thereby providing potential opportunities to test for the formation of host races. TheNortheastPacific galeommatoideanNeaeromya rugiferaattaches to two strikingly different hosts: the blue mud shrimpUpogebia pugettensisand the polychaete sea mouseAphroditaspp. We tested if this host difference has resulted in the formation of host races using shell morphologies and genetic markers. We found that populations from different hosts differ significantly in shell morphology. However, based on mitochondrial makers,N. rugiferashowed no distinct host‐specific genetic structuring, indicating the existence of a panmictic population. We conclude that the host‐specific morphologies these clams exhibit may reflect ecophenotypic plasticity rather than the existence of host races, but this needs to be corroborated with additional genetic data and larger sample sizes. The pronounced conchological variation withinN. rugiferacalls for further investigation of its taxonomic relationship with its poorly studied, but morphologically similar, sympatric congenerNeaeromya compressa.