Sites Of Sympatry Research Articles

Pollinator shifts despite hybridisation in the Cape's hyperdiverse heathers (Erica, Ericaceae).

Interrogating the ecological and geographic factors that influence population divergence dynamics can reveal why some groups of organisms diversify more prolifically than others. One such group is the heathers (Erica, Ericaceae), the largest plant genus in the Cape Floristic Region. We study Erica abietina, a highly variable species complex with four subspecies differing in geographic range, habitat and pollination syndrome. We test for population differentiation, hybridisation, introgression and pollinator-driven divergence using genotyping-by-sequencing on samples across the entire distribution. We find five variably distinct genetic groups, with one subspecies comprising two independent lineages that are geographically isolated and occur on different soil types. Phylogenetic analysis suggests two independent shifts between bird and insect pollination, with accompanying genetic divergence. However, for one pair of populations with different pollinators, we uncover several individuals of hybrid origin at a site of sympatry. These results suggest that floral differentiation driven by divergent selection acts in concert with geographic isolation to maintain reproductive isolation and promote speciation. Our investigations reveal a highly dynamic system whose diversity has been shaped by a variety of interacting forces. We suggest that such a system could be a model for much of the diversification of the Cape flora.

Microhabitat use of northern and southern flying squirrels in a recent hybrid zone

Secondary contact of closely related species may lead to hybridization if reproductive isolation is incomplete. We examined the role of habitat use as a factor contributing to reproductive isolation of northern ( Glaucomys sabrinus (Shaw, 1801)) and southern ( Glaucomys volans (Linnaeus, 1758)) flying squirrels in an area of secondary contact in Ontario, Canada. Specifically, we looked at summer microhabitat use within sites of sympatry and allopatry to test for evidence of reinforcement due to diverging habitat use. We also examined differences in broad-scale habitat features at woodlots to determine predictors of species occurrence across sites. We used 18 years (2002–2019) of flying squirrel summer capture data from six sites along a north–south transect and microhabitat data from vegetation surveys conducted during summer 2016. We found microhabitat variables to be weak predictors of trap-level flying squirrel presence, and we found no evidence of divergence in microhabitat use over the 18 years. Further, we found latitude, not broad-scale habitat, was the strongest predictor of site-level flying squirrel occurrence. Overall, our findings suggest that microhabitat-based isolation is not being reinforced between flying squirrels; however, hybridization may be limited to areas where climate and habitat are suitable for both species.

Correction to: Apis laboriosa confirmed by morphometric and genetic analyses of giant honey bees (Hymenoptera, Apidae) from sites of sympatry in Arunachal Pradesh, North East India

Correction to: Apis laboriosa confirmed by morphometric and genetic analyses of giant honey bees (Hymenoptera, Apidae) from sites of sympatry in Arunachal Pradesh, North East India

Apis laboriosa confirmed by morphometric and genetic analyses of giant honey bees (Hymenoptera, Apidae) from sites of sympatry in Arunachal Pradesh, North East India

Apis laboriosa confirmed by morphometric and genetic analyses of giant honey bees (Hymenoptera, Apidae) from sites of sympatry in Arunachal Pradesh, North East India

Genetic Variability in Balkan Paleoendemic Resurrection Plants Ramonda serbica and R. nathaliae Across Their Range and in the Zone of Sympatry.

The genus Ramonda includes three Paleoendemic and Tertiary relict species that survived in refugial habitats of the Balkan Peninsula (R. nathaliae and R. serbica) and the Iberian Peninsula (R. myconi). They are all “resurrection plants,” a rare phenomenon among flowering plants in Europe. Ramonda myconi and R. nathaliae are diploids (2n = 2x = 48), while R. serbica is a hexaploid (2n = 6x = 144). The two Balkan species occur in sympatry in only two localities in eastern Serbia, where tetraploid potential hybrids (2n = 4x = 96) were found. This observation raised questions about the existence of gene flow between the two species and, more generally, about the evolutionary processes shaping their genetic diversity. To address this question, genetic markers (AFLP) and an estimate of genome size variation were used in a much larger sample and at a larger geographic scale than previously. The combination of AFLP markers and genome size results suggested ongoing processes of interspecific and interploidy hybridization in the two sites of sympatry. The data also showed that interspecific gene flow was strictly confined to sympatry. Elsewhere, both Ramonda species were characterized by low genetic diversity within populations and high population differentiation. This is consistent with the fact that the two species are highly fragmented into small and isolated populations, likely a consequence of their postglacial history. Within sympatry, enormous variability in cytotypes was observed, exceeding most reported cases of mixed ploidy in complex plant species (from 2x to >8x). The AFLP profiles of non-canonical ploidy levels indicated a diversity of origin pathways and that backcrosses probably occur between tetraploid interspecific hybrids and parental species. The question arises whether this diversity of cytotypes corresponds to a transient situation. If not, the question arises as to the genetic and ecological mechanisms that allow this diversity to be maintained over time.

Why may the same species have different elevational ranges at different sites in New Guinea?

Species in mountainous areas have characteristic elevational ranges, but with some variation from site to site. Such variation has been studied extensively elsewhere in the world, but not yet for New Guinea bird species. Hence, we examined five sources of that variation for New Guinea birds: latitude, competition, slope, the Massenerhebung effect, and physical barriers. Decreases of species elevational ranges with latitude are illustrated by three sets of examples: 20 species confined to New Guinea's mountains, but which descend to sea level at higher latitudes in Australia (joined to New Guinea at Pleistocene times of low sea level); 13 sea-level populations of some of the same New Guinea upland species on New Guinea's Fly River bulge; and 11 populations on the Aru Islands (part of Pleistocene New Guinea and Australia). Many New Guinea species contract or expand their elevational ranges, associated with the presence or absence of competing congenerics, which segregate by elevation at sites of sympatry. The flat Karimui Basin at an elevation of 1,110 m illustrates effects of slope, because the basin supports populations of many species otherwise characteristic of the flat lowlands, and lacks populations of many hill forest species characteristic of the sloping terrain found at that elevation elsewhere in New Guinea. We provide three sets of New Guinea examples of the Massenerhebung effect described for mountains elsewhere in the world: shifts of species to higher elevations on large high mountains far from the sea than on small coastal mountains or isolated mountains. Finally, we suggest that very steep high ridges boxing in a watershed on the Foja Mts. constitute dispersal barriers that have prevented 33 species expected at that watershed's elevation from arriving or establishing themselves.

Dietary partitioning in newly sympatric urban flying-foxes (Pteropus poliocephalus and Pteropus alecto)

The black flying-fox (Pteropus alecto) is extending its range southward and is now sympatric with the grey-headed flying-fox (P. poliocephalus) in New South Wales. Competition for food between the two species has been suggested to be a contributor to declines of the vulnerable grey-headed flying-fox. During winter 2016 the diet of both species was investigated over one night at four sites of sympatry, by microscopic analysis of faecal samples. Resource partitioning between the two species was found, with the black flying-fox either preferentially choosing to eat more fruit than the grey-headed flying-fox or being an inferior competitor for pollen and nectar. These results, though limited, do not support the hypothesis that the black flying-fox threatens the grey-headed flying-fox through food competition.

Rapid Loss of Resistance to Satyrization in Invasive Mosquitoes and the Effects of Age on Interspecific Mating Frequency.

In several areas where Aedes aegypti (L.) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) have come in contact following successful invasions, Ae. aegypti have been rapidly displaced by Ae. albopictus. Recent work has confirmed that mating interference, in the form of satyrization, is likely a driving factor in these competitive displacements. However, in sites of sympatry, Ae. aegypti females evolve resistance to satyrization, and in the laboratory, satyrization-susceptible Ae. aegypti can evolve resistance within a few generations of cage exposure to Ae. albopictus. The resistance trait may be costly to maintain, as satyrization-resistant females have been shown to invest more time in mate selection. Here, we show that increased satyrization-resistance does not persist in the absence of satyrization pressure, confirming a cost to maintaining this trait. Ae. aegypti lines that had been previously selected for increased satyrization-resistance demonstrated rapid decreases in this trait over eight generations. Support for the hypothesis that condition-dependent mate preferences lead to variation in mating choice among individuals of differing quality within a population has been accumulating. Here we examine how age-related changes in reproductive effort or reproductive value may result in age-dependent mate choice. We hypothesize that older, lower quality individuals may be more likely to accept a subpar mating, in this case an interspecific mating. Our results demonstrate that mosquito age significantly affects interspecific mating rates with older mosquitoes (male and female) engaging in interspecific mating more frequently than younger counterparts (26.32 vs 9.41%). We discuss the possibility of age-related signal variation causing the breakdown of mating barriers with age.

Trophic overlap between native and invasive stream crayfish

We examined trophic dynamics of a stream food web where invasive Orconectes neglectus appear to be displacing native O. eupunctus in the Spring River drainage of the Ozark Highlands, Missouri and Arkansas, USA. We collected crayfish species and possible food sources seasonally from a site of sympatry on the South Fork Spring River. We determined diet overlap and potential for competition between O. eupunctus and O. neglectus, and investigated seasonal variation using carbon and nitrogen stable isotope analyses and gut content analyses. Gut content analysis showed both species of crayfish consumed mainly detritus during summer and spring, with other prey categories varying by species and season. Stable isotope analysis showed that O. eupunctus and O. neglectus relied on invertebrates as a major energy and nutrient source throughout summer, autumn, and spring, and the two species showed differences in their stable isotope signatures during spring and summer, but not autumn. Given the trophic overlap between O. eupunctus and O. neglectus, there is a potential for the two species to compete for food and to be ecologically redundant. Ecological redundancy can lead to reduced effects on ecosystem function post-invasion, and therefore examining ecological redundancy of potential invaders should be a conservation priority.

Morphological differentiation of Ixodes persulcatus and I. ricinus hybrid larvae in experiment and under natural conditions

The objective of the study was detection of hybrid larvae in Ixodes persulcatus and Ixodes ricinus cohabitation sites. To this end, the following three tasks were solved: interspecies crossing of ticks, evaluation of typical morphological signs of the hybrid larvae, and analysis of collected specimens from sites of sympatry. Under experimental conditions, hybrid larvae of I. persulcatus (female) and I. ricinus (male) were obtained that differed from the parental species by the size of setae on the scutum and alloscutum. Discriminant analysis yielded 87.5% classification accuracy for the priory set groups of I. persulcatus, I. ricinus, and hybrids. Of 88 hybrid larvae, 13 (15%) were classified as I. persulcatus and 4 (5%) as I. ricinus. We measured larvae of Ixodes ticks (n=141) collected from small mammals in 1950–1970 in Karelia in cohabitation sites of these species that were previously classified as I. persulcatus or I. ricinus. According to the results of discriminant analysis, 31 larvae (22%) were classified as hybrids with probability p≥0.52; for 10 larvae (7%), the probability of placement to the hybrid group was >0.95.

Topography as a driver of cryptic speciation in the high-elevation cape sedge Tetraria triangularis (Boeck.) C. B. Clarke (Cyperaceae: Schoeneae)

Since some speciation mechanisms are more likely to generate morphological disparity than others, the general failure of vascular plant taxonomists to recognize cryptic diversity may bias perceptions about speciation process in plants. While the exceptional floristic richness of the South African Cape has largely been attributed to adaptive divergence (‘ecological’ speciation), a combination of climatic dynamism and complex topography has likely provided ample opportunities for ‘non-ecological’ vicariant speciation, a mechanism which is perhaps more likely to produce cryptic species. We explore the role of topography as a driver of ‘non-ecological’ speciation in the high-elevation sedge Tetraria triangularis. Within this species, molecular and morphological data reveal five cryptic or semi-cryptic lineages of Miocene–Pliocene age which qualify as evolutionary species. At least three of these maintain their distinctness in sites of sympatry, identifying them as biological species. Negligible range overlap, and the identification of topography as a significant predictor of range turnover, identifies speciation as allopatric and a result of impeded gene flow across low-elevation topographic features. Weak morphological and ecological divergence implies a limited role for adaptive divergence in powering speciation, with character displacement in sympatry possibly arising as a consequence of interspecific competition. Although we cannot exclude a role for disruptive selection in species differentiation, we identify isolation of populations on topographically separated mountains as the principal motor of speciation. We suggest that the importance of topography in the genesis of Cape floristic diversity has been inadequately acknowledged.

POLLINATOR SPECIFICITY DRIVES STRONG PREPOLLINATION REPRODUCTIVE ISOLATION IN SYMPATRIC SEXUALLY DECEPTIVE ORCHIDS

Few studies have quantified the full range of pre- and postzygotic barriers that limit introgression between closely related plant species. Here, we assess the strength of four isolating mechanisms operating between two morphologically similar and very closely related sympatric orchid taxa, Chiloglottis valida and C. aff. jeanesii. Each taxon sexually attracts its specific wasp pollinator via distinct floral volatile chemistry. Behavioral experiments with flowers and synthetic versions of their floral volatiles confirmed that very strong pollinator isolation is mediated by floral odor chemistry. However, artificially placing flowers of the two taxa in contact proximity revealed the potential for rare interspecific pollination. Although we found hybrid vigor in F1 hybrids produced by hand-crossing, genetic analysis at both nuclear and chloroplast loci showed significant and moderate-to-strong genetic differentiation between taxa. A Bayesian clustering method for the detection of introgression at nuclear loci failed to find any evidence for hybridization across 571 unique genotypes at one site of sympatry. Rather than inhibiting gene flow, postpollination barriers surveyed here show no contribution to overall reproductive isolation. This demonstrates the primacy of pollinators in maintaining species boundaries in these orchids, which display one of the strongest known examples of prepollination floral isolation.

Resource partitioning and niche hyper‐volume overlap in free‐living Pygoscelid penguins

Summary 1. Species potentially competing for the same resource are considered to be able to co‐exist if they occupy different niches. In an apparent example of this, Adélie, Chinstrap and Gentoo penguins all feed predominantly on krill Euphausea superba at certain sites of sympatry in Antarctica and are proposed to exploit different niche hyper‐volumes via differential area and depth utilization. 2. Patterns of foraging for 49 of these penguins breeding in sympatry were assessed using dead‐reckoning loggers to examine foraging niche overlap. 3. Area use overlaps were 0·29 for Adélie ∩ Chinstrap, 0·44 for Adélie ∩ Gentoo, and 0·40 for Chinstrap ∩ Adélie and depth use overlaps were 0·69 for Adélie ∩ Chinstrap, 0·48 for Adélie ∩ Gentoo, and 0·52 for Chinstrap ∩ Gentoo Penguins. 4. Foraging efficiency was greatest for Adélie Penguins diving near surface waters (0–15 m) while Chinstraps were most efficient at medium depths (15–60 m) and Gentoo Penguins most efficient at deeper depths (> 60 m). There appear to be physiological reasons for this. Penguins primarily exploited those depths where they were most efficient. 5. The overlap for foraging periods was 0·47 for Adélie ∩ Chinstrap, 0·26 for Adélie ∩ Gentoo, and 0·40 for Chinstrap ∩ Gentoo Penguins. Chinstraps foraged primarily at night, Gentoos during the morning and Adélies in the afternoon. Temporal differences in foraging may result in the three species exploiting krill at those depths where it is best adapted to pursue it, this being mediated by the diel vertical migration of krill. 6. Integration of all measured parameters together gives minimal overlap between species with total overlaps of 0·09 for Adélie ∩ Chinstrap, 0·05 for Adélie ∩ Gentoo, and 0·08 for Chinstrap ∩ Gentoo Penguins so it appears that these penguins conform to conventional theory in avoiding competition in areas of sympatry. However, a model incorporating prey movement between hyper‐volumes indicates that penguins may still compete, even in the virtual absence of hyper‐volume overlap. 7. This study shows that Pygoscelid penguin do indeed exploit different hypervolumes in areas of sympatry but that such exploitation of different niches by sympatric species feeding on a common resource does not necessarily result in reduced competition if the mobility of prey is high.

A molecular phylogeny of the Sylvia cantillans complex: Cryptic species within the Mediterranean basin

The subalpine warbler Sylvia cantillans is formally considered a polytypic species, with four subspecies, European S. c. cantillans, albistriata, moltonii (recently resumed name: subalpina) and North African S. c. inornata. They are very similar in external morphology but clearly differ in their vocalizations. We evaluated their uncertain taxonomic status reconstructing the phylogenetic and phylogeographic relationships among populations sampled across major biogeographical areas in the European species’ range, using nucleotide sequences of the mitochondrial cytochrome b gene (mtDNA cyt b). A variety of phylogenetic analyses concordantly led to identify four major groups, only partially corresponding to the three European nominal subspecies. Phylogenetic trees showed a monophyletic group including all moltonii individuals, well diverged from all other taxa. Populations taxonomically assigned to cantillans were polyphyletic being split into two distinct clades (western and southern cantillans), with monophyletic albistriata closely related to southern cantillans. Individuals of moltonii and southern cantillans sampled in sites of sympatry in central Italy were assigned to their respective groups, with perfect concordance between phenotypic and genetic identifications. All findings indicate that moltonii should be ranked as a distinct species. Former subspecies cantillans is polyphyletic, but additional data are needed to define the taxonomic status of its two clades. Albistriata is phylogenetically related to southern cantillans and should be provisionally kept as a subspecies of S. cantillans. The cantillans complex thus provides an interesting case-study illustrating geographical structuring across small geographical ranges, and it exemplifies speciation through differentiation in allopatry leading to reproductive isolation after a secondary contact.

The intersection of specialization and speciation

The intersection of specialization and speciation

Host-Plant Specialization in Pheromone Strains of the European Corn Borer Ostrinia nubilalis in France

European corn borer (ECB) feeding on maize (Zea mais), mugwort (Artemisia vulgaris), and hop (Humulus lupulus) are genetically different in France and referred to as host-plant races. Here, we investigated sex pheromone composition as a possible trait linked to the host plant. ECB host races were sampled from 13 different sites in France. GC-MS analysis of female pheromone showed that 175 out of 176 maize females belonged to the Z type with one hybrid. In contrast, mugwort and hop females belonged almost exclusively to the E type. No Z females were found on these plants and only 2 females out of 169 were hybrids. In the three sites of sympatry, the hybrid proportion was far from Hardy-Weinberg expectations. Wind tunnel experiments showed that 76-79% of maize males from three populations were attracted by Z females, whereas neither mugwort nor hop males were. Mugwort males from Toussus-le-Noble were attracted by E females originating from an American maize strain. These data showed that maize, mugwort, and hop host races of O. nubilalis differ not only in their host plant but also in the sex pheromone they use. Because mugwort and hop are putative ancestral host plants, these results are discussed from the point of view of evolutionary scenarios for the emergence of Z and E strains.

A direct regional scale estimate of transgene movement from genetically modified oilseed rape to its wild progenitors.

One of the major environmental concerns over genetically modified (GM) crops relates to transgene movement into wild relatives. The pattern of hybridization ultimately affects the scale and rapidity of ecological change and the feasibility of containment. A new procedure for quantifying hybrid formation over large areas is described. Remote sensing was used to identify possible sites of sympatry between Brassica napus and its progenitor species across 15 000 km2 of south-east England in 1998. Two sympatric populations with B. rapa and one with B. oleracea were found over the entire survey area. Every newly recruited plant in these populations in 1999 was screened for hybrid status using flow cytometry and molecular analyses. One hybrid was observed from the 505 plants screened in the B. rapa populations but none of the nine B. oleracea recruits were hybrids. Measures to minimize gene flow are suggested, and a procedure for the post-release evaluation and containment of GM cultivars is proposed.

The allopolyploid origin of Spiranthes hongkongensis (Orchidaceae)

Morphological and ecological similarities between Spiranthes hongkongensis Hu et Barretto and S. sinensis (Pers.) Ames suggest a close evolutionary relationship. The hypothesis that S. hongkongensis evolved through natural hybridization between S. sinensis and S. spiralis was tested using isozyme electrophoresis. A total of 28 isozyme loci were interpreted in the diploid species S. sinensis and S. spiralis, and “fixed heterozygosity” owing to gene duplication was observed at ten of these loci in S. hongkongensis. Isozyme phenotypes provided strong evidence for an allotetraploid origin of S. hongkongensis, with S. sinensis and most likely S. spiralis as its diploid progenitors. Chromosomal counts of S. hongkongensis gave a tetraploid number of ≈60. The allotetraploid species is self‐fertile, and completely isolated by sterility barriers from S. sinensis. Premating isolation also exists between S. hongkongensis and S. sinensis due to earlier flowering and autogamy in S. hongkongensis, which may account for the rarity of natural hybrids in the sites of sympatry. The role of the autogamous breeding system in the establishment and spread of S. hongkongensis is discussed.

The Allopolyploid Origin of Spiranthes hongkongensis (Orchidaceae)

Morphological and ecological similarities between Spiranthes hongkongensis Hu et Barretto and S. sinensis (Pers.) Ames suggest a close evolutionary relationship. The hypothesis that S. hongkongensis evolved through natural hybridization between S. sinensis and S. spiralis was tested using isozyme electrophoresis. A total of 28 isozyme loci were interpreted in the diploid species S. sinensis and S. spiralis, and “fixed heterozygosity” owing to gene duplication was observed at ten of these loci in S. hongkongensis. Isozyme phenotypes provided strong evidence for an allotetraploid origin of S. hongkongensis, with S. sinensis and most likely S. spiralis as its diploid progenitors. Chromosomal counts of S. hongkongensis gave a tetraploid number of ≈60. The allotetraploid species is self-fertile, and completely isolated by sterility barriers from S. sinensis. Premating isolation also exists between S. hongkongensis and S. sinensis due to earlier flowering and autogamy in S. hongkongensis, which may account for the rarity of natural hybrids in the sites of sympatry. The role of the autogamous breeding system in the establishment and spread of S. hongkongensis is discussed.

Parthenogenetic Cnemidophorus tesselatus Complex at Higbee, Colorado: Resolution of 30 Years of Controversy

At times over 30 years, various authors have expressed conflicting opinions on the composition of the parthenogenetic Cnemidophorus tesselatus complex at Higbee, Otero County, Colorado, the only known site of sympatry between diploid and triploid members of this complex. Recently, some workers have stated that two rather than three distinctive parthenogens occur at Higbee, one being an undescribed triploid species (tentatively designated pattern class C), which resulted from hybridization between C. tesselatus D(2n) and gonochoristic C. sexlineatus. Alternatively, our study identified two diploid pattern classes [C(2n) and D(2n)] and one triploid pattern class [B(3n)] among specimens of C. tesselatus from Higbee (including those with electrophoretically determined ploidy levels). We used two canonical variate analyses (CVA) to test hypotheses concerning the identity and origin of the triploid form. CVA1 suggested that specimens of the Higbee triploid form represented C. tesselatus B(3n), not an undescribed species. CVA2 suggested that C. tesselatus B(3n) was derived from a C. tesselatus C(2n) x C. sexlineatus hybrid, not a hybrid involving C. tesselatus D(2n).