Sympatric Locations Research Articles

Geographic variation of host use in the leaf beetle Agelasa nigriceps suggests host range expansion

Host range expansion is an important event in the evolution of host use in phytophagous insects. Herein, we report geographic variation of host use in the chrysomelid leaf beetle, Agelasa nigriceps Motschulsky (Coleoptera: Chrysomelidae), and suggest that this beetle is expanding its host range. This beetle has been recently recorded on Pterostyrax hispidus Sieb. et Zucc. (Styracaceae) in addition to its common host plant Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. (Actinidiaceae). The A. arguta-associated populations were widely found in Japan, whereas the P. hispidus-associated populations were found only in central and southwestern Japan. In the present study, we examined adult feeding behavior and larval performance of 12 A. nigriceps populations collected from eight localities, four localities where beetles occurred only on A. arguta (allopatric localities) and four localities where A. arguta- and P. hispidus-associated populations occurred sympatrically (sympatric localities). Beetles of all populations, irrespective of their host plants and localities, showed high acceptance of and high larval performance on A. arguta leaves. In contrast, we found considerable variation in the beetle response to P. hispidus leaves. The A. arguta-associated populations of allopatric localities scarcely accepted P. hispidus leaves, whereas those of sympatric localities, particularly those of P. hispidus-associated populations, accepted and grew on P. hispidus leaves, although the degree of acceptance and larval performance varied among localities. These results strongly suggest that A. arguta is the ancestral host for A. nigriceps, and host range expansion to the P. hispidus has occurred in this beetle.

Predominant regeneration strategy results in species-specific genetic patterns in sympatric Nothofagus s.s. congeners (Nothofagaceae)

Life-history traits affect plant performance. Predominant regeneration modes, sprouting v. non-sprouting, will result in contrasting evolutionary and ecological responses that may be traced by nuclear markers. Sympatric Nothofagus Blume species provide the natural setting to test whether sprouters have a greater ability to maintain genetic diversity. In total, 28 populations along the entire distribution range of N. antarctica (G. Forst.) Oerst. were screened by eight polymorphic isozyme loci. We compared pairwise genetic patterns of the predominant sprouter N. antarctica with the mainly non-sprouter N. pumilio (Poepp. & Endl.) Krasser at 20 sympatric locations along their geographically concordant widespread range. Overall, the sprouter N. antarctica showed higher genetic variation throughout its range than did the non-sprouter N. pumilio. Mid-latitude populations of N. antarctica have maintained isozyme diversity, as inferred using genetic-landscape analysis. Despite the potential for inter-specific gene flow and past hybridisations, species identity was preserved by divergent selective forces acting on sympatric populations with distinct autoecological traits. Predominantly sprouting, as compared with mainly non-sprouting, has favoured long-term persistence of genet diversity in relatively large populations that were probably less affected by drift through time, thereby preserving molecular variants along its range. These variants, in combination with plasticity in diverse habitats, have resulted in greater resilience of N. antarctica under changing scenarios.

Sympatry between Two Wide-ranging Salamander Species

Understanding how closely related species coexist remains a central problem in community ecology. Habitat characteristics, presence of predators and competitors, and frequency of disturbance all affect the geographic distribution of a species. Plethodon cinereus and P. electromorphus are two closely related and ecologically similar species that have a large geographic overlap in their distributions. In this study, I had two main goals. First, I wanted to determine how commonly sympatric locations occurred between these two species. To address this goal, I conducted landscape-scale surveys in areas that should contain sympatric locations based on their distributions. My second goal was to determine if the relative number of individuals of each species within sympatric locations was stable over time by monitoring four sympatric locations over three years. In addition, flooding occurred during one year of the study, impacting two of the four monitored sympatric locations; therefore, I wanted to examine whether this disturbance affected the salamander populations at those locations. This flooding event provided a rare opportunity to study the impact of flooding on terrestrial salamanders, a topic about which little is known. I found that sympatric locations occurred less frequently than expected by chance and that some sympatric sites seem to be relatively stable while at others, the relative population size of P. cinereus was increasing — and that this shift might be positively affected by flooding. While this study demonstrated that P. cinereus and P. electromorphus do not occur in sympatry as frequently as expected by chance, the cause for this result is unknown. The most likely factor is that the two species exhibit subtle habitat differences that have not yet been demonstrated. The interactions between P. cinereus and P. electromorphus are complex, and the patterns observed here could have been generated by any number of mechanisms. Further research on this system could clarify some of these remaining questions.

The divergence of two independent lineages of an endemic Chinese gecko, Gekko swinhonis, launched by the Qinling orogenic belt

The genetic structure and demographic history of an endemic Chinese gecko, Gekko swinhonis, were investigated by analysing the mitochondrial cytochrome b gene and 10 microsatellite loci for samples collected from 27 localities. Mitochondrial DNA data provided a detailed distribution of two highly divergent evolutionary lineages, between which the average pairwise distance achieved was 0.14. The geographic division of the two lineages coincided with a plate boundary consisting of the Qinling and Taihang Mts, suggesting a historical vicariant pattern. The orogeny of the Qinling Mts, a dispersal and major climatic barrier of the region, may have launched the independent lineage divergence. Both lineages have experienced recent expansion, and the current sympatric localities comprised the region of contact between the lineages. Individual-based phylogenetic analyses of nucDNA and Bayesian-clustering approaches revealed a deep genetic structure analogous to mtDNA. Incongruence between nucDNA and mtDNA at the individual level at localities outside of the contact region can be explained by the different inheritance patterns and male-biased dispersal in this species. High genetic divergence, long-term isolation and ecological adaptation, as well as the morphological differences, suggest the presence of a cryptic species.

Parallel evolution of character displacement driven by competitive selection in terrestrial salamanders

BackgroundParallel evolution can occur when common environmental factors exert similar selective forces on morphological variation in populations in different geographic localities. Competition can also generate morphological shifts, and if competing species co-occur in multiple geographic regions, then repeated instances of competitively-driven morphological divergence (character displacement) can occur. Despite the importance of character displacement for inferring the role of selection in morphological evolution however, replicated instances of sympatric morphological divergence are understudied.ResultsI tested the hypothesis that interspecific competition generated patterns of parallel morphological divergence in multiple geographic locations where two competing salamander species, Plethodon jordani and P. teyahalee, come into contact. I used geometric morphometrics to characterize head shape and found ecological character displacement in sympatric localities on each of three distinct mountains (geographic transects), where sympatric specimens displayed greater cranial differences and an increase in cranial robustness as compared to allopatric specimens. Using a recently developed analytical procedure, I also found that the observed morphological evolution within each species was consistent among transects; both in the total amount of morphological change as well as the direction of evolution in the morphological data space. This provided strong statistical evidence of parallel morphological evolution within species across replicate geographic transects.ConclusionsThe results presented here reveal that the morphological evolution of each species followed a common evolutionary path in each transect. Because dispersal between sympatric locations among transects is unlikely, these findings suggest that the repeated instances of character displacement have evolved in situ. They also suggest that selection from competitive interactions plays an important role in initiating sympatric morphological divergence in these species, and drives parallel sympatric morphological divergence between species.

Two sympatric spotted gum species are molecularly homogeneous

Large fruited spotted gum eucalypt Corymbia henryi occurs sympatrically with small fruited spotted gum Corymbia citriodora subspecies variegata over a large portion of its range on the east coast of Australia. The two taxa are interfertile, have overlapping flowering times and share a common set of insect and vertebrate pollinators. Previous genetic analysis of both taxa from two geographically remote sites suggested that the two were morphotypes rather than genetically distinct species. In this study we further explore this hypothesis of genic species by expanding sampling broadly through their sympatric locations and examine local-scale spatial genetic structure in stands that differ in species and age composition. Delineation of populations at five microsatellite loci, using an individual-based approach and Bayesian modelling, as well as clustering of individuals based on allele frequencies showed the two species to be molecularly homogeneous. Genetic structure aligned largely with geographic areas of origin, and followed an isolation-by-distance model, where proximal populations were generally less differentiated than more distant ones. At the stand level, spotted gums also generally showed little structure consistent with the high levels of gene flow inferred across the species range. Disturbances in the uniformity of structuring were detected, however, and attributed to localised events giving rise to even aged stands, probably due to regeneration from a few individuals following fire.

Interspecific Agonistic Behaviors in a Salamander Community: Implications for Alpha Selection

Competition between closely related species can affect behavioral interactions. Intense interspecific competition may favor the evolution of elevated levels of interspecific aggression, termed alpha selection. Salamanders of the genus Plethodon exhibit territorial aggression, and in some cases interference mechanisms may have evolved under the process of alpha selection. Throughout Ohio, two closely related and ecologically similar species of salamander, Plethodon cinereus (red-backed salamander) and P. electromorphus (northern ravine salamander), occur in similar habitats and can be found in sympatry. However, the occurrence of syntopic areas is infrequent compared to the range overlap of each species and seems to be limited by factors other than broad geographic factors. Here, we used salamanders from allopatric and sympatric locations to examine the behavior of both species toward interspecific intruders. We hypothesized that animals in sympatry would exhibit heightened aggression compared to salamanders from allopatric areas. We found support for this hypothesis, indicating that intense interference competition may occur between P. cinereus and P. electromorphus in sympatry. Further, our results are consistent with the hypothesis of alpha selection at the level of behavioral aggression. These results suggest that sympatry may represent an unstable equilibrium where neither species can gain a competitive advantage.

Genetic Variation Within Two Sympatric Spotted Gum Eucalypts Exceeds Between Taxa Variation

Abstract Population substructure and hybridization, among other factors, have the potential to cause erroneous associations in linkage disequilibrium (LD) mapping. Two closely related spotted gum eucalypts, Corymbia variegata and C. henryi (Myrtaceae) occur in sympatry in the east coast of Australia and potentially interbreed. They are morphologically similar but are distinguished as separate species based on capsule and foliage size. To determine whether they hybridize in nature and its implications for LD mapping, we investigated the level of molecular divergence between the two species at two sympatric locations separated by 300 kilometres. Very few individuals of intermediate morphology were identified, despite the two species occurring only metres apart. Analysis of genetic structure using 12 microsatellite loci showed that genetic differentiation between populations of the same species at different locations (FST = 0.07 for both species; p = 0.0001) was significantly higher than that observed between species at each location (mean FST = 0.02 and 0.04 for Cherry tree and Bunyaville respectively; p = 0.0001; all Mann-Whitney U-test p ≤ 0.01). No species-specific alleles or significant allele frequency differences were detected within a site, suggesting recurr#ent local gene flow between the two species. The lack of significant allele frequency differences implies no population stratification along taxonomic lines. This suggested that there is little concern for cryptic hybridization when sampling from sites of sympatry for LD mapping.

Hybridization between Ischnura graellsii (Vander Linder) and 2. elegans (Rambur) (Odonata: Coenagrionidae): are they different species?

Two closely related damselflies, Ischnura graellsii and I. elegans, were analysed for morphological differences and reproductive isolation in the north coast of Galicia (NW Spain). We compared animals from sympatric and allopatric localities, including I. elegans from Belgium and I. graellsii from southern Spain as pure allopatric populations. A set of morphometric characters were studied by means of multivariate discriminant analysis to determine if these two species can be unambiguously distinguished. Discriminant analysis revealed that I. graellsii and I. elegans are well differentiated on the first two axis (86% and 11%, respectively). I. graellsii individuals are distinguished from I. elegans by their smaller size and, specifically, by their narrower and shorter wings and shorter tibiae. In addition, I. elegans has a narrower space between the branches of each cercus, and greater distance between the branches of each paraproct. Sympatric individuals are morphologically intermediate, suggesting hybridization. When the species were put together in the laboratory, they showed partial temporal separation in mating behaviour, but males of I. elegans readily mated with females of I. graellsii, and hybrid individuals were obtained. The opposite heterospecific cross was almost impossible, apparently because of mechanical problems with the tandem linkage. Laboratory-reared hybrids (from male I. elegans ¥ female I. graellsii) are morphologically intermediate, mainly resembling the maternal phenotype. Although hybridization between both taxa is common, we suggest maintaining the specific status for both phenotypes because they show incipient reproductive isolation, as it is reported in the literature. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76, 225‐235. ADDITIONAL KEYWORDS: hybrids ‐ morphological differentiation ‐ Odonata ‐ reproductive barriers ‐ speciation.

EVIDENCE OF REINFORCEMENT OF PREMATING ISOLATION BETWEEN TWO SPECIES OF THE GENUS OCHTHEBIUS (COLEOPTERA: HYDRAENIDAE)

The increase in premating reproductive isolation between recently diverged and potentially interbreeding taxa resulting from selection against hybridization (reinforcement) is one of the most contentious issues in evolutionary biology. After many years of debate, its plausibility under various conditions has been shown by theoretical studies and some cases have been documented. At present, interest is arising about the frequency and importance of reinforcement in nature. Ochthebius quadricollis and Ochthebius sp. A are two hydraenid beetles inhabiting marine rock pools in the Mediterranean basin. By molecular analysis of a contact zone between the two species along the Italian Tyrrhenian coast, full reproductive isolation between the two species was evidenced. However, the finding of introgressed specimens at some diagnostic loci suggested that gene flow occurred in the past but then ceased. In this article, by analyzing species composition of mating couples collected in sympatric localities, we show the existence of strong assortative mating between the two species in nature. In laboratory multiple-choice mating trials, sympatric populations showed greater assortative mating than allopatric populations. Reinforcement is suggested as the most parsimonious hypothesis to explain the evolution of discriminative mate recognition systems occurring among O. quadricollis and Ochthebius sp. A under sympatric, but not allopatric, populations.

Location‐specific sympatric morphological divergence as a possible response to species interactions in West VirginiaPlethodonsalamander communities

1. The competitive interactions of closely related species have long been considered important determinants of community composition and a major cause of phenotypic diversification. However, while patterns such as character displacement are well documented, less is known about how local adaptation influences diversifying selection from interspecific competition. 2. We examined body size and head shape variation among allopatric and sympatric populations of two salamander species, the widespread Plethodon cinereus and the geographically restricted P. nettingi. We quantified morphology from 724 individuals from 20 geographical localities throughout the range of P. nettingi. 3. Plethodon nettingi was more robust in cranial morphology relative to P. cinereus, and sympatric localities were more robust relative to allopatric localities. Additionally, there was significantly greater sympatric head shape divergence between species relative to allopatric communities, and sympatric localities of P. cinereus exhibited greater morphological variation than sympatric P. nettingi. 4. The sympatric morphological divergence and increase in cranial robustness of one species (P. nettingi) were similar to observations in other Plethodon communities, and were consistent with the hypothesis of interspecific competition. These findings suggest that interspecific competition in Plethodon may play an important role in phenotypic diversification in this group. 5. The increase in among-population variance in sympatric P. cinereus suggests a species-specific response to divergent natural selection that is influenced in part by other factors. We hypothesize that enhanced morphological flexibility and ecological tolerance allow P. cinereus to more rapidly adapt to local environmental conditions, and initial differences among populations have allowed the evolutionary response of P. cinereus to vary across replicate sympatric locations, resulting in distinct evolutionary trajectories of morphological change.

Niche shifts and local competition between two coral reef fishes at their geographic boundary

Competition theory predicts that, when resources are limiting, interacting species should differ more in resource use where they co-occur, compared with where they do not (resource partitioning). The damselfishes Dascyllus aruanus and D. melanurus provide a useful test of this prediction because they exhibit largely allopatric geographic ranges that overlap near Port Moresby, Papua New Guinea. To test whether this species pair exhibited responses in resource use that were consistent with competition theory, the depth distributions, coral substrata and diet of each species at allopatric and sympatric locations were compared. Where sympatric, the frequency of co-occurrence was examined and foraging ranges and diet on corals where the species do and do not co-occur were compared. Contrary to expectations, the species were more similar in depth, habitat use and diet in the sympatric region. Within this location, they sometimes co-existed in the same coral shelters, but much less often than would be expected with random assortment. Where they did co-exist, their diets converged. D. melanurus exhibited restricted foraging ranges and consumed smaller prey in the presence of D. aruanus, but not vice versa. It was concluded that niche shifts along different resource axes at the geographic boundary are explained both by large-scale constraints in resource availability and local-scale competitive interactions.

Long-term occurrence of hybrids between Japan Sea and Pacific Ocean forms of threespine stickleback, Gasterosteus aculeatus, in Hokkaido Island, Japan

The distribution patterns of two genetically divergent forms (Japan Sea and Pacific Ocean forms) of Gasterosteus aculeatus and their hybrids in the Hokkaido Island, Japan were investigated. Hybrid frequencies and the mating pattern of natural F1-hybrids and backcrosses, were examined by using allozyme analysis. The distribution patterns matched those previously reported. All three sympatric localities in eastern Hokkaido Island included hybrids between the two forms in each year examined. A low frequency of hybrids of sticklebacks has been maintained in areas of sympatry of the two forms in Hokkaido Island for several years. The proportion of F1-hybrids was significantly lower than expected by random mating in six samples from four sympatric populations, suggesting form-assortative mating. Mating crosses of natural F1-hybrids existed in both patterns. Natural F1-hybrids backcrossed more frequently with Pacific Ocean form than Japan Sea form. However, the proportions of backcross individuals in two of three samples were not significantly different from the expected proportions by random mating between F1-hybrids and their parent forms. In other samples, despite the Pacific Ocean form predominant in a population, F1-hybrid predominantly backcrossed with the Japan Sea form. These results support the hypothesis of gene flow from Pacific Ocean to Japan Sea forms.

CHARACTER DISPLACEMENT AND ECOMORPHOLOGICAL ANALYSIS OF TWO LONG-EARED MYOTIS (M. AURICULUS AND M. EVOTIS)

Ecomorphological analysis was used to evaluate ecological relationships between 2 species of bats, Myotis auriculus and M. evotis. We imaged jaws and skulls of 242 specimens from 20 localities within the range of both taxa, emphasizing their southwestern regional area of sympatry. Using traditional morphometric and geometric morphometric methods, values for characters taken from dentaries of both species were analyzed in detail. Both methods detected character displacement and allowed us to detect differences in jaw size and shape within both species. The morphological difference in jaw shape is more emphasized within sympatric populations of M. evotis than in M. auriculus. This may indicate that competitive selection acts more on M. evotis. At sympatric localities, M. evotis displayed a shift to a more specialized trophic state with a trophic architecture (more highly placed articular process and robust molars) likely better at capturing beetles, whereas M. auriculus may have a greater advantage for capturing soft-bodied prey such as moths. On the other hand, the articular process is located lower relative to the toothrow of the dentary in M. auriculus. Also the shape of the jaw in this species suggests a weaker bite, more shearing force, and wider gape. All shape differences in jaw morphology are emphasized in sympatry, confirming active competitive interactions between these 2 species.

Habitat preferences of tree pipit (Anthus trivialis) and meadow pipit (A. pratensis) at sympatric and allopatric localities

Habitat preferences of the tree pipit (Anthus trivialis) and the meadow pipit (A. pratensis; Passeriformes: Motacillidae) were observed during the years 1998–1999 at three localities in the Czech Republic; two with one pipit species only, and a third with both species present. We investigated one of the possible mechanisms allowing syntopic coexistence—different habitat selection. We characterised territories of each pipit pair by the habitats present in the territory (defined by dominant plant composition) and by quantitative parameters (territory size, height and density of the vegetation, number of look-outs of different height categories, and proportion of wet ground). Tree pipits preferred significantly higher vegetation of lower density than meadow pipits, and there was generally a higher number of high look-outs in their territories. However, in some of the preferred territories at the allopatric locality of the tree pipit, steep hill slopes could well substitute for higher look-outs, which were almost absent. The two pipit species at the sympatric locality occupied very different habitats, which was also reflected in quantitative parameters of their territories. The available data of pipit habitat at different European localities show that the two species can occupy a much wider range of habitats. The habitat separation in sympatry might therefore be one of the mechanisms allowing syntopic coexistence of both species.

Character Displacement in Stag Beetles (Coleoptera: Lucanidae)

I quantitatively analyzed male morphology of two closely related stag beetles species (Odontolabis mouhoti Hope and O. cuvera Parry) in 11 allopatric and two sympatric locations in the Asian tropics and subtropics. Across allopatric locations, body size and genitalia size nearly completely overlapped between O. mouhoti and O. cuvera, and body color was more similar between the two species in allopatric locations. In sympatric locations the differences between the two species in these characters were highly noticeable, genitalia size being most signiÞcant. The body color difference between the two species was most striking in sympatric locations. It is probable that the interaction between the two species induced character displacement in sympatry. Character displacement may enable species to maintain themselves as integrated units by minimizing interspeciÞc competition and enhancing reproductive isolation.

Molecular genetic analysis of two taxa of the Pleurotus eryngii complex: P. eryngii (DC.Fr.) Quèl. var. eryngii and P. eryngii (DC.Fr.) Quèl. var. ferulae

With the use of isozymes and PCR-fingerprinting analysis molecular markers were found between the varieties Pleurotus eryngii var. eryngii and P. eryngii var. ferulae within the Pleurotus eryngii complex, which allowed the identification of the fruitbodies collected in Southern and Central Italy. The study of sympatric localities has shown that there is no gene exchange between them in the field. The post-mating barriers between these taxa are not yet completely efficient. However, in the field the gene pools of the two taxa appear isolated and associated with specific host plants: Eryngium campestre and Ferula communis. On the basis of the genetic and ecological differences observed and given the absence of gene exchange in sympatric localities, P. eryngii and P. ferulae are to be considered distinct biological species.

Character Displacement in Giant Rhinoceros Beetles

I quantitatively analyzed male morphology of two closely related rhinoceros beetles species (Chalcosoma caucasus F. and Chalcosoma atlas L.) in 12 allopatric and seven sympatric locations throughout Southeast Asia. The qualitative features and the magnitude of intraspecific variation of each species were unaltered between allopatric and sympatric locations. Across allopatric locations, body size, horn size, dimorphic dimension, and genitalia size nearly completely overlapped between C. caucasus and C. atlas. Yet, in all sympatric locations, the differences between the two species in these characters were highly significant. While the enlarged difference between the two species in body size in sympatry could be attributed to habitat differentiation, that in genitalia size far exceeded what was expected from the general body-size displacement. These results indicate that morphological character displacement in sympatry was most complete in sexual organs. This may account for the process of existing species conserving themselves as integrated units by avoiding interspecific competition and enhancing reproductive isolation.

Character Displacement in Giant Rhinoceros Beetles

I quantitatively analyzed male morphology of two closely related rhinoceros beetles species (Chalcosoma caucasus F. and Chalcosoma atlas L.) in 12 allopatric and seven sympatric locations throughout Southeast Asia. The qualitative features and the magnitude of intraspecific variation of each species were unaltered between allopatric and sympatric locations. Across allopatric locations, body size, horn size, dimorphic dimension, and genitalia size nearly completely overlapped between C. caucasus and C. atlas. Yet, in all sympatric locations, the differences between the two species in these characters were highly significant. While the enlarged difference between the two species in body size in sympatry could be attributed to habitat differentiation, that in genitalia size far exceeded what was expected from the general body‐size displacement. These results indicate that morphological character displacement in sympatry was most complete in sexual organs. This may account for the process of existing species conserving themselves as integrated units by avoiding interspecific competition and enhancing reproductive isolation.

Differences in morphology and reproductive traits of Galerucella nymphaeae from four host plant species

AbstractThe water lily beetle Galerucella nymphaeae L. (Coleoptera: Chrysomelidae) exploits different hosts, including Nuphar lutea Sm. and Nymphaea alba L. (both Nymphaeaceae), as well as Polygonum amphibium L. and Rumex hydrolapathum Hudson (both Polygonaceae). The present study investigates whether within‐species differences in morphological and reproductive traits are associated with differences in host species exploitation. A total of 1103 adult beetles were collected from 11 localities in The Netherlands, one of which contained all four hosts and three other localities contained hosts from both families (sympatric localities). Adults originating from Nuphar and Nymphaea were on average darker in colour and larger in size and had disproportionally bigger mandibles than beetles originating from Polygonum and Rumex across the 11 localities. Head capsules of first instar larvae from Nymphaeaceae hosts were between 17% and 28% larger than those of larvae from Polygonaceae hosts. Furthermore, beetles from Nuphar and Nymphaea laid larger sized eggs, but fewer eggs per clutch than beetles originating from Polygonum and Rumex. Although host related variation was less pronounced at the sympatric localities than in the allopatric localities, differences in larval and adult size were still highly significant at the sympatric localities. It is not clear whether the observed differences are genetically based, as opposed to host induced. However, leaf toughness varied among species in a way suggesting that leaf toughness may be partly responsible for host related differences in G. nymphaeae.