Related Sympatric Species Research Articles

Wild or domesticated? An ancient DNA approach to canid species identification in South Africa's Western Cape Province

The fragmentary remains typical of archaeological fauna can prove impossible to identify when confronted with closely related sympatric species. In southern Africa domesticated dogs ( Canis familiaris) and black-backed jackals ( Canis mesomelas) pose just such a problem, rendering difficult an accurate assessment of the timing of arrival of domesticated dogs in the region. Contextual evidence has suggested that canid remains from four Later Stone Age archaeological sites were likely to be domesticated dogs rather than jackals, and were subjected to ancient DNA analyses to determine species. Every tested specimen proved to derive from black-backed jackals. These data provide not only an unexpected window on southern African prehistory, but also highlight the value in applying ancient DNA techniques to archaeological species identification.

Gender Differences in Species Recognition and the Evolution of Asymmetric Sexual Isolation

Closely related sympatric species are expected to evolve strong species discrimination because of the reinforcement of mate preferences. Fitness costs of heterospecific matings are thought to be higher in females than in males, and females are therefore expected to show stronger species discrimination than males. Here, we investigated gender and species differences in sexual isolation in a sympatric species pair of Calopteryx damselflies. The genus Calopteryx is one of the classic examples of reproductive character displacement in evolutionary biology, with exaggerated interspecific differences in the amount of dark wing coloration when species become sympatric. Experimental manipulation of the extent of dark wing coloration revealed that sexual isolation results from both female and male mate discrimination and that wing melanization functions as a species recognition character. Female choice of conspecific males is entirely based on wing coloration, whereas males in one species also use other species recognition cues in addition to wing color. Stronger species discrimination ability in males is presumably an evolutionary response to an elevated male predation risk caused by conspicuous wing coloration. Gender differences in species discrimination and fitness costs of male courtship can thus shed new light on the evolution of asymmetric sexual isolation and the reinforcement of mate preferences.

Evidence of reproductive isolation among closely related sympatric species of Serrasalmus (Ostariophysii, Characidae) from the Upper Madeira River, Amazon, Bolivia

The delimitation of the Serrasalmus species (Characiformes, Serrasalminae) from the Bolivian Amazon (Amazonas, Madeira) was examined using intron length polymorphism assessed by EPIC‐PCR. The six pairs of primers provided 16 polymorphic loci across the species of the region and the allelic diversity ranged between two and 10 alleles per locus. For each locus, the lack of departure from Hardy‐Weinberg expectations in a large number of the populations analysed and the homogenous distribution of linkage disequilibrium between paralogous loci and loci belonging to different intronic systems provided strong lines of evidence that the 16 amplified loci constituted independent neutral markers. Furthermore, allelic diversity was size‐dependent, thereby indicating that insertion‐deletions occurred frequently but randomly in introns, and that intron length polymorphism was a valid marker for investigating the systematics of piranhas. EPIC‐PCR demonstrated that eight of the nine nominal species of piranha of the Upper Madeira were reproductively isolated and identified a new species that differed from its closest morphological and genetic relatives by seven diagnostic or semi‐diagnostic loci. By contrast, no diagnostic or semi‐diagnostic locus was found between S. spilopleura and S. eigenmanni, nor were their allelic frequencies different, thereby questioning the validity of their biological species status, at least in the Upper Madeira. This study, which was one of the first applications of EPIC‐PCR to a large‐scale molecular systematic purpose, demonstrates that it is a rapid, reliable and cost‐effective tool for elucidating issues pertaining to fish systematics.

Recent Evolution of the Human Pathogen Cryptococcus neoformans by Intervarietal Transfer of a 14-Gene Fragment

The availability of the whole-genome sequence from the 2 known varieties of the human pathogenic fungus Cryptococcus neoformans provides an opportunity to study the relative contribution of divergence and introgression during the process of speciation in a genetically tractable organism. At the genomic level, these varieties are nearly completely syntenic, share approximately 85-90% nucleotide identity, and are believed to have diverged approximately 18 MYA. Via a comparative genomic approach, we identified a 14-gene region (approximately 40 kb) that is nearly identical between the 2 varieties that resulted from a nonreciprocal transfer event from var. grubii to var. neoformans approximately 2 MYA. The majority of clinical and environmental var. neoformans strains from around the world contain this sequence obtained from var. grubii. This introgression event likely occurred via an incomplete intervarietal sexual cycle, creating a hybrid intermediate where mobile elements common to both lineages mediated the exchange. The subsequent duplication in laboratory strains of a fragment of this same genomic region supports evolutionary theories that instabilities in subtelomeric regions promote adaptive evolution through gene amplification and subsequent adaptation. Along with a more ancient predicted transfer event in C. neoformans and a recently reported example from Saccharomyces cerevisiae, these data indicate that DNA exchange between closely related sympatric varieties or species may be a recurrent theme in the evolution of fungal species. It further suggests that although evolutionary divergence is the primary force driving speciation, rare introgression events also play a potentially important role.

Fitness correlates of male coloration in a Lake Victoria cichlid fish

Sexual selection by female choice has contributed to the rapid evolution of phenotypic diversity in the cichlid fish species flocks of East Africa. Yet, very little is known about the ecological mechanisms that drive the evolution of female mating preferences. We studied fitness correlates of male nuptial coloration in a member of a diverse Lake Victoria cichlid lineage, Pundamilia nyererei. In this species, male red coloration is subject to intraspecific sexual selection by female mate choice. Male nuptial coloration plays a critical role also in reproductive isolation between this species and the closely related sympatric species P. pundamilia. Here, we show that P. nyererei male coloration is carotenoid based, illustrating the potential for honest signaling of individual quality. In a wild population, we found that variation in male coloration was not associated with variation in a set of strongly intercorrelated indicators of male dominance: male size, territory size, and territory location. Instead, the 2 male characters that predominantly determine female choice, territory size and red coloration, may be independent predictors of male quality: males with bright red coloration and large territories had lower parasite infestation rates. As a result, female preferences tended to select against heavily parasitized males. Consistent with parasite-mediated sexual selection, males had higher and more variable parasite loads than females.

Feeding Ecology of Sympatric Mouse Lemur Species in Northwestern Madagascar

We performed a comparative pilot study on vertical space use and feeding ecology of 2 closely related sympatric mouse lemur species in northwestern Madagascar. We recorded feeding behavior and the use of vertical forest strata for 6 gray and 4 golden-brown mouse lemur females that we followed for 120 h. We carried out feeding experiments and analyzed fecal samples for food remains. Both species showed no significant difference in use of forest strata. They had a similar overall diet, with insect secretions and gum as main plant food resources; arthropod remains occurred in about half of all fecal samples. Both lemurs used in common >50% of the plant species that each consumed, which accounts for ≥70% of all individual plants used. However, both species used >40% of their feeding plant species exclusively and seemed to differ in their degree of specialization on certain plant species.

Specificity of the crowding response in the Brachionus plicatilis species complex

Crowding chemicals influence a wide variety of life history traits in zooplankton communities. In the rotifer Brachionus, sexual reproduction (mixis) is induced by a chemical signal produced by the rotifers that accumulates during population growth. The specificity of the reaction to the mixis induction signal could play a central role in maintaining reproductive barriers between closely related sympatric species. Using cross-induction assays between different species, we tested whether this signal has diversified in the Brachionus plicatilis species complex. We found that closely related, as well as more distant species in this complex, could induce mixis in each other. This suggests that there are no species barriers in sex induction and that the mixis signal did not diversify for several million years during the evolution of the Brachionus plicatilis complex. This apparent stasis is remarkable because pre- and postmating isolation is common in this species complex and, due to its cosmopolitan distribution, species often occur in sympatry.

Comparative analysis of life-history traits in two species of C alomys (Rodentia: Sigmodontinae) in captivity / Analyse comparative des traits d'histoire de vie de deux espèces de Calomys (Rodentia: Sigmodontinae) en captivité

AbstractWe analyzed life-history traits (fertility, growth and rate of postnatal development) in captive-bred colonies of two closely related sympatric species: Calomys expulsus and C. tener (Rodentia, Sigmodontinae). We found significant differences between the species in growth rate and several reproductive traits. C. tener had a smaller litter size and litter mass, smaller proportion of litter mass to maternal mass, lower growth rate and higher infant mortality. We also found an apparent difference in correlation patterns of life history parameters between the two species of Calomys . The strong correlation between body size and fecundity found in other studies of life history traits and in selection experiments seems to be disrupted in C. tener . We found a significant positive correlation between maternal mass and litter size and mass only for C. expulsus, which means that in C. tener the fertility of females does not depend strongly on body mass. We discuss inbreeding depression and stress reactions as possible reasons for these results.

Comparative analysis of life-history traits in two species of C alomys (Rodentia: Sigmodontinae) in captivity / Analyse comparative des traits d'histoire de vie de deux espèces de Calomys (Rodentia: Sigmodontinae) en captivité

AbstractWe analyzed life-history traits (fertility, growth and rate of postnatal development) in captive-bred colonies of two closely related sympatric species: Calomys expulsus and C. tener (Rodentia, Sigmodontinae). We found significant differences between the species in growth rate and several reproductive traits. C. tener had a smaller litter size and litter mass, smaller proportion of litter mass to maternal mass, lower growth rate and higher infant mortality. We also found an apparent difference in correlation patterns of life history parameters between the two species of Calomys . The strong correlation between body size and fecundity found in other studies of life history traits and in selection experiments seems to be disrupted in C. tener . We found a significant positive correlation between maternal mass and litter size and mass only for C. expulsus, which means that in C. tener the fertility of females does not depend strongly on body mass. We discuss inbreeding depression and stress reactions as possible reasons for these results.

Reproductive strategies of sub-Antarctic lithodid crabs vary with habitat depth

We present the first fecundity and egg size data for three species of lithodid crab from Antarctic waters south of the Polar Front, caught in the fisheries operating around the island of South Georgia. In all species, fecundity was observed to increase with body size, but reproductive allocation was found to differ significantly between species. The highest relative fecundity (eggs−g body weight) and smallest egg size was found in Paralomis spinosissima, which is found in shallower waters, whereas the lowest relative fecundity values and largest eggs were recorded in the deeper living species, Neolithodes diomedeae. Evidence is presented that closely related sympatric species may employ quite different reproductive strategies that suit their depth distribution whilst indicating the overriding evolutionary adaptation of reproductive traits to temperature and food availability.

Genetic homogeneity in eight freshwater populations of Sicyopterus lagocephalus, an amphidromous gobiid of La Réunion Island

In the subfamily Sicydiinae of the family Gobiidae, the species Sicyopterus lagocephalus is one of the common amphidromous fish inhabiting island freshwaters in a large intertropical area, widespread from the Comoros archipelago to the Austral Islands. Eight of the main perennial rivers of La Reunion Island (Mascarene Islands) were sampled in 2000, in order to describe their population genetic structure. A total of 267 adult specimens of S. lagocephalus were screened for 14 enzymatic systems providing 15 presumptive loci, 11 of them being polymorphic. Four other loci were useful as diagnostic markers between S. lagocephalus and Cotylopus acutipinnis, a similar, closely related sympatric species. Both species constitute an economic resource locally called “bichique”. The focus of this study, S. lagocephalus, accounts for the majority of the bichique. The results clearly showed a genetic homogeneity among the eight samples (Fst tests). Within-samples tests (Fis) indicated, in general, a heterozygote deficiency. The multidimensional diagrams (CA) describe an overall structure composed of two main subgroups. This structure was not confirmed in a 2001 sampling. The interpretation of the results takes into account the biological life cycle of this species, characterized by a planktonic phase, from hatching to recruitment, followed by a freshwater life of the adults. All the samples in the survey belong to a single pool. However, the young fish entering the rivers are probably of complex origin. We did not find any isolation between rivers and this result should be considered when conservation measures are taken to prevent overfishing.

MARINE RAIATIONS AT SMALL GEOGRAPHIC SCALES: SPECIATION IN NEOTROPICAL REEF GOBUIES (ELACATINUS)

Studies of speciation in the marine environment have historically compared broad-scale distributions and estimated larval dispersal potential to infer the geographic barriers responsible for allopatric speciation. However, many marine clades show high species diversity in geographically restricted areas where barriers are not obvious and estimated dispersal potential should bring many sister taxa into contact. Genetic differentiation at small (separation < 1000 km) spatial scales could facilitate speciation by mechanisms other than the gradual accumulation of reproductive isolation during extended allopatry, such as ecological adaptation to local environmental conditions or the rapid evolution of genes tied to mate recognition, but the role of each of these possibilities has not been simultaneously explored for any species-rich marine taxon. Here, we develop a robust phylogenetic framework for 31 taxa from a species-rich group of Neotropical reef fishes (Gobiidae: Elacatinus) using 3230 bp from one mitochondrial and two nuclear gene regions. We use this framework to explore the contribution of large- and small-scale geographic isolation, ecological differentiation, and coloration toward the formation and maintenance of species. Although species of Elacatinus occur on both sides of the Isthmus of Panama, no sister species are separated by this barrier. Instead, our results indicate that sister taxa occur within oceans. Sister taxa usually differ by coloration, and more distantly related sympatric species frequently differ by resource use. This suggests that some combination of coloration and ecological differences may facilitate assortative mating at range boundaries or in sympatry. Overall, speciation in Elacatinus is consistent with a model of recurring adaptive radiations in stages taking place at small geographic scales.

MARINE RADIATIONS AT SMALL GEOGRAPHIC SCALES: SPECIATION IN NEOTROPICAL REEF GOBIES (ELACATINUS)

Studies of speciation in the marine environment have historically compared broad-scale distributions and estimated larval dispersal potential to infer the geographic barriers responsible for allopatric speciation. However, many marine clades show high species diversity in geographically restricted areas where barriers are not obvious and estimated dispersal potential should bring many sister taxa into contact. Genetic differentiation at small (separation <1000 km) spatial scales could facilitate speciation by mechanisms other than the gradual accumulation of reproductive isolation during extended allopatry, such as ecological adaptation to local environmental conditions or the rapid evolution of genes tied to mate recognition, but the role of each of these possibilities has not been simultaneously explored for any species-rich marine taxon. Here, we develop a robust phylogenetic framework for 31 taxa from a species-rich group of Neotropical reef fishes (Gobiidae: Elacatinus) using 3230 bp from one mitochondrial and two nuclear gene regions. We use this framework to explore the contribution of large- and small-scale geographic isolation, ecological differentiation, and coloration toward the formation and maintenance of species. Although species of Elacatinus occur on both sides of the Isthmus of Panama, no sister species are separated by this barrier. Instead, our results indicate that sister taxa occur within oceans. Sister taxa usually differ by coloration, and more distantly related sympatric species frequently differ by resource use. This suggests that some combination of coloration and ecological differences may facilitate assortative mating at range boundaries or in sympatry. Overall, speciation in Elacatinus is consistent with a model of recurring adaptive radiations in stages taking place at small geographic scales.

Ultraviolet plumage reflectance distinguishes sibling bird species

Realistic studies of plumage color need to consider that many birds can see near-UV light, which normal humans cannot perceive. Although previous investigations have revealed that UV-based plumage reflectance is an important component of various intraspecific social signals, the contribution of UV signals to inter-specific divergence and speciation in birds remains largely unexplored. I describe an avian example of an interspecific phenomenon in which related sympatric species that appear similar to humans (sibling species) differ dramatically in the UV. Both UV video images and physical reflectance spectra indicate that the dorsal plumage of the tanager Anisognathus notabilis has a strong UV-limited reflectance band that readily distinguishes this species from its sibling congener Anisognathus flavinuchus. The main human-visible distinction between A. notabilis (olive back) and coexisting A. flavinuchus (black back) also occurs among different geographic populations of A. flavinuchus. Notably, however, olive- and black-backed taxa interbreed (differentiated populations of A. flavinuchus) unless the additional UV distinction is present (A. notabilis vs. A. flavinuchus). Thus, UV-based reflectance can be an essential component of plumage divergence that relates to reproductive isolation, a key attribute of biological species.

Are both sympatric species Ilex perado and Ilex canariensis secretly hybridizing? Indication from nuclear markers collected in Tenerife

BackgroundIntra-specific and intra-individual polymorphism is frequently observed in nuclear markers of Ilex (Aquifoliaceae) and discrepancy between plastid and nuclear phylogenies is the rule in this genus. These observations suggest that inter-specific plastid or/and nuclear introgression played an important role in the process of evolution of Ilex. With the aim of a precise understanding of the evolution of this genus, two distantly related sympatric species collected in Tenerife (Canary Islands), I. perado and I. canariensis, were studied in detail. Introgression between these two species was previously never reported. One plastid marker (the atpB-rbcL spacer) and two nuclear markers, the ribosomal internal transcribed spacer (ITS) and the nuclear encoded plastid glutamine synthetase (nepGS) were analyzed for 13 and 27 individuals of I. perado and I. canariensis, respectively.ResultsThe plastid marker is intra-specifically constant and correlated with species identity. On the other hand, whereas the nuclear markers are conserved in I. perado, they are highly polymorphic in I. canariensis. The presence of pseudogenes and recombination in ITS sequences of I. canariensis explain this polymorphism. Ancestral sequence polymorphism with incomplete lineage sorting, or past or recent hybridization with an unknown species could explain this polymorphism, not resolved by concerted evolution. However, as already reported for many other plants, past or recent introgression of an alien genotype seem the most probable explanation for such a tremendous polymorphism.ConclusionsData do not allow the determination with certitude of the putative species introgressing I. canariensis, but I. perado is suspected. The introgression would be unilateral, with I. perado as the male donor, and the paternal sequences would be rapidly converted in highly divergent and consequently unidentifiable pseudogenes. At least, this study allows the establishment of precautionary measures when nuclear markers are used in phylogenetic studies of genera having experienced introgression such as the genus Ilex.

Differential parental care behaviors of arboreal and terrestrial microhylid frogs from Papua New Guinea

I studied the ecology of parental care behaviors displayed by two closely related sympatric species of microhylid frogs in Papua New Guinea that occupy different microhabitats. Adult removal experiments on the terrestrial frog Hylophorbus rufescens and the undescribed arboreal frog Oreophryne sp. “A” demonstrate a significant positive effect of parental attendance on offspring survivorship and differential causes of egg mortality between microhabitats. Desiccation was the primary cause of egg mortality for the arboreal frog, whereas predation was the main source of mortality for the terrestrial frog. These selection pressures (desiccation and predation) are comparable to two of Wilson’s “prime movers” of the evolution of parental care (harsh environment and predation) and may have driven and/or are maintaining the evolution of parental care behaviors in these Papuan microhylid frogs. These results highlight microhabitat-specific selection pressures in the evolution and maintenance of parental care behaviors.

Divergent selection during speciation of Lake Malawi cichlid fishes inferred from parallel radiations in nuptial coloration.

Repeated evolution of the same phenotypic difference during independent episodes of speciation is strong evidence for selection during speciation. More than 1,000 species of cichlids, >10% of the world's freshwater fish species, have arisen within the past million years in Lakes Malawi and Victoria in eastern Africa. Many pairs of closely related sympatric species differ in their nuptial coloration in very similar ways. Nuptial coloration is important in their mate choice, and speciation by sexual selection on genetically or ecologically constrained variation in nuptial coloration had been proposed, which would repeatedly produce similar nuptial types in different populations, a prediction that was difficult to test in the absence of population-level phylogenies. We measured genetic similarity between individuals within and between populations, species, and lake regions by typing 59 individuals at >2,000 polymorphic genetic loci. From these data, we reconstructed, to our knowledge, the first larger species level phylogeny for the most diverse group of Lake Malawi cichlids. We used the genetic and phylogenetic data to test the divergent selection scenario against colonization, character displacement, and hybridization scenarios that could also explain diverse communities. Diversity has arisen by replicated radiations into the same color types, resulting in phenotypically very different, yet closely related, species within and phenotypically highly similar yet unrelated sets of species between regions, which is consistent with divergent selection during speciation and is inconsistent with colonization and character displacement models.

Mitochondrial Restriction-Site Characterization of a Brazilian Group of Eyelid-Less Gymnophthalmid Lizards

Phylogenetic relationships among eight Brazilian genera of the lizard family Gymnophthalmidae were analyzed using mitochondrial DNA restriction-site data. The intergeneric relationships inferred from a cladistic analysis of 32 restriction sites were widely congruent with a recent phylogenetic analysis based on morphology. Assuming a molecular clock of 2% MY, these gymnophthalmid lizards may have diverged from a common ancestor some 7–8 MYA. The monophyly of the five eyelid-less microteiid genera from the Rio São Francisco Quaternary sand dunes was also supported by mitochondrial data, and the time estimated for this radiation was about 2–3 MYA. The mtDNA data also suggest that the unisexual population of Gymnophthalmus underwoodi from Roraima is not originated by hybridization between its two closely related sympatric bisexual species Gymnophthalmus leucomystax and Gymnopohthalmus vanzoi, in accordance with previous biochemical and karyotypic data.

Behavioural plasticity in relation to egg and time limitation: the case of two fly species in the genus Anastrepha (Diptera: Tephritidae)

Reproductive opportunities in insects that deposit their eggs in discrete resource patches are frequently limited because the availability of oviposition substrates is often spatially and temporally restricted. Such environmental variability leads individuals to confront time‐ or egg‐limitation constraints. Additionally, species with different oviposition strategies (i.e. single egg layers vs clutch layers) commonly deal with different structural and ecological characteristics of larval host plants. To test the hypothesis that oviposition strategies such as laying eggs singly or in batches (clutches) are related to these constraints (i.e. egg vs time limitation), we compared the lifetime oviposition patterns of two closely related sympatric species of Anastrepha (Diptera: Tephritidae) with different oviposition strategies. We exposed five cohorts of A. obliqua and A. ludens females, over the course of their adult lifetimes, to three conditions of “habitat quality” (measured as host density per cage): unpredictable habitat quality (host density varied randomly from day to day between 1, 5, 15, 30 and 60 hosts/cage), low habitat quality (fixed density of one host/cage) and high habitat quality (fixed density of 60 hosts/cage). Responses to host density conditions were strikingly different in the two species. (1) Frequency of host visits and oviposition events increased in A. obliqua but not in A. ludens when host densities increased. (2) Anastrepha ludens females accepted low quality hosts (i.e. fruits on which eggs had already been laid and were therefore partially covered with host marking pheromone) significantly more often than A. obliqua females did. (3) Females of A. obliqua adjusted their oviposition activity to variations in host density, whereas A. ludens females exhibited a constant oviposition pattern (i.e. did not respond to variations in host density). Based on the above, it is likely that in A. obliqua oviposition is governed by egg‐limitation and in A. ludens by time‐limitation constraints. We discuss the relationship between the oviposition strategies of each fly species and the fruiting phenology and density of their native host plants. We also address the possible influence of oogenesis modality and parasitism by braconid wasps in shaping oviposition behaviour in these insects.

Morphological variation and the definition of species in the snake genus Tropidophis (Serpentes, Tropidophiidae)

SYNOPSIS. Historically, the definition of species in the Neotropical snake genus Tropidophis has been difficult because of intraspecific variation in scalation and a paucity of specimens of most taxa. There were 13 species recognized at the time of t he last review in 1960, but additional species have since been discovered and a taxonomic review and update is needed. Data on morphological variation are presented here and used to clarify the status of the described taxa. Because many taxa are allopatr ic with their closest relatives, it is necessary to make decisions as to their status as species or subspecies. As a gauge of spec ies status in the genus, character divergence in ten pairs of closely related sympatric species was examined. Typically, such species are differentiated by two non-overlapping colour pattern differences, often in combination with a diagnostic (non-overlapping) or overlapping difference in scalation. Using this criterion, seven taxa previously considered as subspecies are here elevated to species status, whereas seven other taxa are retained as subspecies, although in some cases they are allocated to different spe cies. As a result, the genus Tropidophis is considered here to comprise 29 species, 26 of which are West Indian and 15 of those are restricted to Cuba.