Niche conservatism and spread explain introgression between native and invasive fish.

Hybridisation can be an important driver of evolutionary change, but hybridisation with invasive species can have adverse effects on native biodiversity. While hybridisation has been documented across taxa, there is limited understanding of ecological factors promoting patterns of hybridisation and the spatial distribution of hybrid individuals. We combined the results of ecological niche modelling (ENM) and restriction site-associated DNA sequencing to test theories of niche conservatism and biotic resistance on the success of invasion, admixture, and extent of introgression between native and non-native fishes. We related Maxent predictions of habitat suitability based on the native ranges of invasive Eastern Banded Killifish (Fundulus diaphanus diaphanus Lesueur 1817) and native Western Banded Killifish (Fundulus diaphanus menona Jordan and Copeland 1877) to admixture indices of individual Banded Killifish. We found that Eastern Banded Killifish predominated at sites predicted as suitable from their ENM, consistent with niche conservatism. Admixed individuals were more common as Eastern Banded Killifish habitat suitability declined. We also found that Eastern Banded Killifish were most common at sites closest to the presumed source of this invasion, whereas the proportion of admixed individuals increased with distance from the source of invasion. Lastly, we found little evidence that habitat suitability for Western Banded Killifish provides biotic resistance from either displacement by, or admixture with, invasive Eastern Banded Killifish. Our study demonstrates that ENMs can inform conservation-relevant outcomes between native and invasive taxa while emphasising the importance of protecting isolated Western Banded Killifish populations from invasive conspecifics.

Discovery of facultative parthenogenesis in a new world crocodile.

Over the past two decades, there has been an astounding growth in the documentation of vertebrate facultative parthenogenesis (FP). This unusual reproductive mode has been documented in birds, non-avian reptiles-specifically lizards and snakes-and elasmobranch fishes. Part of this growth among vertebrate taxa is attributable to awareness of the phenomenon itself and advances in molecular genetics/genomics and bioinformatics, and as such our understanding has developed considerably. Nonetheless, questions remain as to its occurrence outside of these vertebrate lineages, most notably in Chelonia (turtles) and Crocodylia (crocodiles, alligators and gharials). The latter group is particularly interesting because unlike all previously documented cases of FP in vertebrates, crocodilians lack sex chromosomes and sex determination is controlled by temperature. Here, using whole-genome sequencing data, we provide, to our knowledge, the first evidence of FP in a crocodilian, the American crocodile, Crocodylus acutus. The data support terminal fusion automixis as the reproductive mechanism; a finding which suggests a common evolutionary origin of FP across reptiles, crocodilians and birds. With FP now documented in the two main branches of extant archosaurs, this discovery offers tantalizing insights into the possible reproductive capabilities of the extinct archosaurian relatives of crocodilians and birds, notably members of Pterosauria and Dinosauria.

Insights into genetic variation and demographic history of sharpnose rays: examinations of three species of Telatrygon (Elasmobranchii, Dasyatidae) from the Indo-West Pacific.

Coastal and demersal chondrichthyans (sharks, rays, and skates) are expected to exhibit high levels of genetic differentiation in areas of complex geomorphology. Population genetic studies investigating the extent to which demographic history shapes the genetic structure of these fishes are rare. Here, we combined mitochondrial DNA (Cytb and ND2) and 8 nuclear microsatellite loci from 244 individuals to examine the population genetic structure and demographic history of the 3 Indo-West Pacific species of sharpnose rays (Telatrygon zugei, Telatrygon biasa, and Trygon crozieri). High levels of genetic variation both within and between species were identified. Phylogenetic analysis partitioned haplotypes into 2 lineages supporting divergence of T. zugei from T. crozieri and T. biasa during the Pleistocene. Furthermore, microsatellite-based clustering analyses identified 4 genetic groups (i.e. T. zugei from Japan, T. zugei from coastal China, T. biasa from Gulf of Thailand, and T. crozieri from the Andaman Sea). Measurements of genetic differentiation also support these 4 groups. Additionally, Pleistocene demographic expansions were examined in all genetic groups. The climate oscillations and current hydrologic cycles in the Indo-West Pacific appear to coincide with the hypothesis regarding speciation and the observed demographic history trends of the sharpnose rays. Considering the species group has, until recently, been thought to be one species, these results are critical for defining management units and guiding conservation efforts to preserve stingray biodiversity.

Breeding behaviour predicts patterns of natural hybridization in North American minnows (Cyprinidae).

Premating barriers such as variation in reproductive behaviour can evolve quickly, but because gametic and postzygotic incompatibilities often evolve more slowly, circumstances that bring gametes into contact can breach the boundaries of premating isolation. In aquatic environments, the gametes of organisms with external fertilization are released into a constantly moving environment and may come into contact with heterospecific gametes. In fishes, nest association (spawning in another species' nest) is a behaviour that brings gametes from different species into close spatiotemporal proximity. These interactions might increase chances of hybridization, especially when multiple species associate with a single nest builder. This study addresses these interactions in the largest clade of North American freshwater fishes, the minnows (Cyprinidae). We compiled a list of over 17,000 hybrid specimens in conjunction with species distribution data, breeding behaviours, and an inferred phylogeny to test if breeding behaviour, in addition to evolutionary history, is an important predictor of hybridization. We find that breeding behaviour is a significant predictor of hybridization, even when phylogenetic relatedness and divergence time are accounted for. Specifically, nest associates are more likely to hybridize with other nest associates whereas non-nesting species had relatively low rates of hybridization.

Evolutionary patterns of diadromy in fishes: more than a transitional state between marine and freshwater.

BACKGROUND: Across the tree of life there are numerous evolutionary transitions between different habitats (i.e., aquatic and terrestrial or marine and freshwater). Many of these dramatic evolutionary shifts parallel developmental shifts that require physiological, anatomical and behavioral changes for survival and reproduction. Diadromy (scheduled movement between marine and freshwater) has been characterized as a behavior that acts as an evolutionary intermediate state between marine and freshwater environments, implying that diadromous lineages are evolutionarily transient. This hypothesis comes with assumptions regarding the rates of evolutionary transitions in and out of diadromy as well as rates of speciation and extinction in diadromous fishes. RESULTS: Based on a published phylogeny of 7822 species of ray-finned fishes, state speciation and extinction models of evolutionary transition between marine, freshwater, and diadromous species suggest transition rates out of diadromy are 5-100 times higher that transition between marine and freshwater or into diadromy. Additionally, high speciation and low extinction rates separate diadromous fishes from marine and freshwater species. As a result, net diversification (net diversification = speciation - extinction) is about 7-40 times higher in diadromous fishes compared to freshwater and marine respectively. Together the transition, speciation, and extinction rates suggest diadromy is the least stable of the three states. CONCLUSION: Evolutionary transitions to diadromy are rare in fishes. However, once established, diversification rates in diadromous lineages are high compared to both marine and freshwater species. Diadromous lineages tend to be more transient than marine or freshwater lineages and are found to give rise to marine and freshwater specialists in addition to diadromous descendants. Although diadromy is not a necessary evolutionary intermediate between marine and freshwater, these results support the interpretation of diadromy as an important, occasionally intermediate state, that contributes to biodiversity in fishes in all environments. This evolutionary instability of diadromous lineages is counteracted by their relatively high diversification rates. These findings highlight the importance of integrating the dynamics of diversification and major evolutionary transitions for understanding macroevolutionary patterns.

Improved methods for capture, extraction, and quantitative assay of environmental DNA from Asian bigheaded carp (Hypophthalmichthys spp.).

Indirect, non-invasive detection of rare aquatic macrofauna using aqueous environmental DNA (eDNA) is a relatively new approach to population and biodiversity monitoring. As such, the sensitivity of monitoring results to different methods of eDNA capture, extraction, and detection is being investigated in many ecosystems and species. One of the first and largest conservation programs with eDNA-based monitoring as a central instrument focuses on Asian bigheaded carp (Hypophthalmichthys spp.), an invasive fish spreading toward the Laurentian Great Lakes. However, the standard eDNA methods of this program have not advanced since their development in 2010. We developed new, quantitative, and more cost-effective methods and tested them against the standard protocols. In laboratory testing, our new quantitative PCR (qPCR) assay for bigheaded carp eDNA was one to two orders of magnitude more sensitive than the existing endpoint PCR assays. When applied to eDNA samples from an experimental pond containing bigheaded carp, the qPCR assay produced a detection probability of 94.8% compared to 4.2% for the endpoint PCR assays. Also, the eDNA capture and extraction method we adapted from aquatic microbiology yielded five times more bigheaded carp eDNA from the experimental pond than the standard method, at a per sample cost over forty times lower. Our new, more sensitive assay provides a quantitative tool for eDNA-based monitoring of bigheaded carp, and the higher-yielding eDNA capture and extraction method we describe can be used for eDNA-based monitoring of any aquatic species.

Genetic signatures of a demographic collapse in a large-bodied forest dwelling primate (Mandrillus leucophaeus).

It is difficult to predict how current climate change will affect wildlife species adapted to a tropical rainforest environment. Understanding how population dynamics fluctuated in such species throughout periods of past climatic change can provide insight into this issue. The drill (Mandrillus leucophaeus) is a large-bodied rainforest adapted mammal found in West Central Africa. In the middle of this endangered monkey's geographic range is Lake Barombi Mbo, which has a well-documented palynological record of environmental change that dates to the Late Pleistocene. We used a Bayesian coalescent-based framework to analyze 2,076 base pairs of mitochondrial DNA across wild drill populations to infer past changes in female effective population size since the Late Pleistocene. Our results suggest that the drill underwent a nearly 15-fold demographic collapse in female effective population size that was most prominent during the Mid Holocene (approximately 3-5 Ka). This time period coincides with a period of increased dryness and seasonality across Africa and a dramatic reduction in forest coverage at Lake Barombi Mbo. We believe that these changes in climate and forest coverage were the driving forces behind the drill population decline. Furthermore, the warm temperatures and increased aridity of the Mid Holocene are potentially analogous to current and future conditions faced by many tropical rainforest communities. In order to prevent future declines in population size in rainforest-adapted species such as the drill, large tracts of forest should be protected to both preserve habitat and prevent forest loss through aridification.