Frog Complex Research Articles

Unravelling male advertisement call variability in the brown tree frog (Litoria ewingii) complex by using citizen science

In the face of global biodiversity declines, conservation measures are urgently needed. However, our lack of knowledge on species’ diversity, distributions and population trends presents a major obstacle, particularly for morphologically cryptic species. Field surveys to gather this information present a logistical challenge, but the rapid rise of citizen science presents a new opportunity, generating huge volumes of data rapidly across a species’ range. We use data from a national citizen-science project to document the distribution and advertisement call variability in a group of five morphologically conserved treefrogs. Using 542 male advertisement calls across the entire range of five species, we found considerable levels of acoustic variation both among and within species. Note shape, notes per call and positions of the longest and shortest notes were most useful to delineate species. Our research will assist in species delineation and identification in the field and form the basis for a more accurate understanding of species diversity and distributions in the brown tree frog complex. We also demonstrated the utility of citizen science in documenting species distributions and diversity.

Multiple Transitions between Y Chromosome and Autosome in Tago's Brown Frog Species Complex.

Sex chromosome turnover is the transition between sex chromosomes and autosomes. Although many cases have been reported in poikilothermic vertebrates, their evolutionary causes and genetic mechanisms remain unclear. In this study, we report multiple transitions between the Y chromosome and autosome in the Japanese Tago's brown frog complex. Using chromosome banding and molecular analyses (sex-linked and autosomal single nucleotide polymorphisms, SNPs, from the nuclear genome), we investigated the frogs of geographic populations ranging from northern to southern Japan of two species, Rana tagoi and Rana sakuraii (2n = 26). Particularly, the Chiba populations of East Japan and Akita populations of North Japan in R. tagoi have been, for the first time, investigated here. As a result, we identified three different sex chromosomes, namely chromosomes 3, 7, and 13, in the populations of the two species. Furthermore, we found that the transition between the Y chromosome (chromosome 7) and autosome was repeated through hybridization between two or three different populations belonging to the two species, followed by restricted chromosome introgression. These dynamic sex chromosome turnovers represent the first such findings in vertebrates and imply that speciation associated with inter- or intraspecific hybridization plays an important role in sex chromosome turnover in frogs.

Systematics of the Lao torrent frog, Amolops cremnobatus Inger & Kottelat, 1998 (Anura: Ranidae), with descriptions of four new species

Abstract The Lao torrent frog Amolops cremnobatus Inger & Kottelat, 1998 was recently hypothesized, based on mitochondrial DNA, to consist of more than a single species across its range in Laos and flanking regions of Vietnam and Thailand. We tested this hypothesis using mitochondrial DNA, nuclear DNA, and quantitative and qualitative morphological data from adults and larvae. We found corroborating lines of evidence for five distinct evolutionary lineages that we hypothesize to be species. Amolops cremnobatus sensu stricto is restricted to the southeastern portion of its previous range, and remaining populations are described as four new species. Some of the new species are easier to diagnose with morphology as larvae than as adults. Further sampling in northern Thailand may reveal an additional species of this torrent frog complex.

Phylogeography, hybrid zones and contemporary species boundaries in the south-eastern Australian smooth frogs (Anura: Myobatrachidae: Geocrinia)

Paleo-climatic fluctuations have driven episodic changes in species distributions, providing opportunities for populations to diverge in isolation and hybridise following secondary contact. Studies of phylogeographic diversity and patterns of gene flow across hybrid zones can provide insight into contemporary species boundaries and help to inform taxonomic and conservation inferences. Here we explore geographic diversity within the acoustically divergent yet morphologically conserved south-eastern Australian smooth frog complex and assess gene flow across a narrow hybrid zone using mitochondrial nucleotide sequences and nuclear genome-wide single nucleotide polymorphisms. Our analyses reveal the presence of an evolutionarily distinct taxon restricted to the Otway Plains and Ranges, Victoria, which forms a narrow (9–30 km wide), spatiotemporally stable (>50 years) hybrid zone with Geocrinia laevis, which we describe herein as a new species.

Population structure, mate choice, and genome transmission in naturally formed pairs in a Pelophylax lessonae–Pelophylax esculentus hybridogenetic system

Central European water frog Pelophylax esculentus is a hybrid that lives sympatrically and forms genetic systems with one of its parental species, in this case L-E (P. lessonae - P. esculentus). Hybrids are restored in each generation due to hybridogenesis, a unique mode of hemiclonal reproduction. We investigated changes in the species composition, mate choice, and genome transmission in naturally formed pairs in the L-E hybridogenetic system from the Raków fish pond complex (SW Poland). Our observations showed that the genetic system remained the same for over a decade but the share of the taxa and the sex ratios within the species changed. The frequency of P. lessonae decreased by about 20% in favor of P. esculentus. The proportion of males to females of P. lessonae increased twofold and of P. esculentus fourfold. We also found that the stability of the L-E population was ensured by a specific female mate choice pattern with the dominance of homotypic P. lessonae and heterotypic ♀P. esculentus × ♂P. lessonae pairs (almost 90% of the pairs collected from nature). The youngest females and males that formed a successful amplexus were 3 years old. We noted a male-male competition manifested by the exclusion of young males (before the third hibernation) from the participation in the mating. An analysis of genome transmission to gametes revealed that females P. lessonae transmitted Lx, while P. esculentus transmitted the Rx and/or Lx genomes. Males of P. lessonae transmitted the Lx or Ly genomes, while P. esculentus transmitted the Lx, Ly, and/or Rx genomes. The high proportion of the L genomes transferred to gametes enables both the restoration of the parental species P. lessonae and the regular renewal of a new generation of hybrids.Significance statementCentral European water frog complex includes two species: Pelophylax ridibundus (genotype RR) and P. lessonae (LL), and their natural hybrid, P. esculentus (RL). Hybrid individuals of both sexes reproduce due to a specific mode of reproduction, i.e., hybridogenesis, in which hybrids eliminate one of the parental genomes (R or L) from the germ line prior to meiosis and transmit the other one (not recombined, i.e., clonal) to the gametes. The hybrids live in mixed populations with one of the parental species and are restored in each generation. This, in turn, allows a kind of balance to be maintained in a population due to specific mate choice and genome transmission. Our research showed that the stability of the studied population was ensured by female preference to P. lessonae and male-male competition manifested by the exclusion of males under 3 years of age from the participation in the mating.

Geographic peculiarities of structure and hemicloning reproduction of Pelophylax esculentus water frog complex (Anura, Ranidae) populations in the East European Plain within Ukraine

Abstract Geographic peculiarities of population structure and hemicloning reproduction of the water frog Pelophylax esculentus complex of 904 samples within southern East European Plain were analyzed. The proportion of populations of P. ridibundus is 0.667 against those 0.042 of P. lessonae. The RE-type populations are the most common among mixed ones (0.153). The colonies of the two parental species and P. kl. esculentus (REL-type), as well as those of P. lessonae with P. kl. esculentus (LE-type), have the frequencies 0.072 and 0.046, respectively. All-hybrid populations (E-type) are not numerous across the region (0.017). In the populations of Central, Northern and Western Ukraine, the P. lessonae genome is eliminated during gametogenesis within hybrids while in the Lower Dnieper and Lower Danube drainages, genome of P. ridibundus is eliminated. In the Eastern Ukraine populations, hybrids usually produce diploid gametes or haploid gametes with the P. ridibundus genome, less often with the chromosome set of P. lessonae only, and even more rarely a mixture of different types of gametes. The predominance of P. ridibundus in hybrid communities and the elimination of the P. lessonae genome in hybrids inevitably leads to the transformation of hybrid populations into “pure” R-type populations. This circumstance makes hybridization with P. ridibundus a factor in the shrinking of P. lessonae populations. That trend is especially expressed in the Forest steppe zone, where hybridization proceeds most intensively, the P. lessonae genome is eliminated in hybrids, and unstable populations with a numerical superiority of P. ridibundus predominate.

Ecological divergence and synchronous Pleistocene diversification in the widespread South American butter frog complex

Phylogeographic studies primarily focus on the major role of landscape topography in driving lineage diversification. However, populational phylogeographic breaks may also occur as a result of either niche conservatism or divergence, in the absence of geographic barriers to gene flow. Furthermore, these two factors are not mutually exclusive and can act in concert, making it challenging to evaluate their relative importances on explaining genetic variation in nature. Herein, we use sequences of two mitochondrial and four nuclear genes to investigate the timing and diversification patterns of species pertaining to the Leptodactylus latrans complex, which harbors four morphologically cryptic species with broad distributions across environmental gradients in eastern South America. The origin of this species complex dates back to the late Miocene (ca. 5.5 Mya), but most diversification events occurred synchronically during the late Pleistocene likely as the result of ecological divergence driven by Quaternary climatic oscillations. Further, significant patterns of environmental niche divergences among species in the L. latrans complex imply that ecological isolation is the primary mode of genetic diversification, mostly because phylogenetic breaks are associated with environmental transitions rather than topographic barriers at both species and populational scales. We provided new insights about diversification patterns and processes within a species complex of broadly and continuously distributed group of frogs along South America.

The genomics of mimicry: Gene expression throughout development provides insights into convergent and divergent phenotypes in a Müllerian mimicry system.

A common goal in evolutionary biology is to discern the mechanisms that produce the astounding diversity of morphologies seen across the tree of life. Aposematic species, those with a conspicuous phenotype coupled with some form of defence, are excellent models to understand the link between vivid colour pattern variations, the natural selection shaping it, and the underlying genetic mechanisms underpinning this variation. Mimicry systems in which multiple species share the same conspicuous phenotype can provide an even better model for understanding the mechanisms of colour production in aposematic species, especially if comimics have divergent evolutionary histories. Here we investigate the genetic mechanisms by which vivid colour and pattern are produced in a Müllerian mimicry complex of poison frogs. We did this by first assembling a high‐quality de novo genome assembly for the mimic poison frog Ranitomeya imitator. This assembled genome is 6.8 Gbp in size, with a contig N50 of 300 Kbp R. imitator and two colour morphs from both Ranitomeya fantastica and R. variabilis which R. imitator mimics. We identified a large number of pigmentation and patterning genes that are differentially expressed throughout development, many of them related to melanocyte development, melanin synthesis, iridophore development and guanine synthesis. Polytypic differences within species may be the result of differences in expression and/or timing of expression, whereas convergence for colour pattern between species does not appear to be due to the same changes in gene expression. In addition, we identify the pteridine synthesis pathway (including genes such as qdpr and xdh) as a key driver of the variation in colour between morphs of these species. Finally, we hypothesize that genes in the keratin family are important for producing different structural colours within these frogs.

Comparative mapping of a new repetitive DNA sequence and chromosome region-specific probes unveiling rearrangements in an Amazonian frog complex.

The frog species Physalaemus ephippifer exists in the Amazonian region and harbors heteromorphic Z and W chromosomes. A genetic lineage closely related to this species was recognized based on its mitochondrial DNA and RADseq-style markers, but its taxonomic status is still unclear and has been referred to as Lineage 1 of "P. cuvieri". The heteromorphic sex chromosomes found in P. ephippifer are not present in this lineage and which of its chromosome pairs is homologous to the sex chromosomes of P. ephippifer remain to be elucidated as well as the role of such a karyotypic divergence in the evolution of these frogs. Here, we described a new family of repetitive DNA and used its chromosomal sites along with the markers detected by a probe constructed from the microdissected segment of the Z chromosome of P. ephippifer to infer chromosomal homology. We also analyzed an unnamed species that is considered to be the sister group of the clade composed of Lineage 1 of "P. cuvieri" and P. ephippifer. Our results suggest that complex rearrangements involving the chromosomes that were inferred to be homeologous to the sex chromosomes of P. ephippifer have occurred during the divergence of this group of frogs.

Age and growth in an anuran hybrid zone: Fitness-related traits of the diploid/polyploid ground frog complex (genus Odontophrynus) from central Argentina

Diploid Odontophrynus cordobae and tetraploid Odontophrynus americanus coexist in syntopy in central Argentina, and recently a hybrid zone between them with numerous triploid individuals has been reported. Furthermore, hybrid polyploids with odd numbers of chromosome sets often exhibit low viability and fertility. Our aim was to test differences in age-related life history aspects influencing fitness in hybrids and their parental species, by comparing demographic and growth-related parameters. The mean age and snout-vent length at sexual maturity and adulthood did not differ significantly among taxa. Longevity and potential reproductive lifespan were one year higher in O. cordobae than O. americanus and hybrids. We did not find significant differences in growth parameters among taxa. Our study shows similar patterns of size and demographics parameters. Triploid hybrids have a similar longevity and viability to parental species. The age structure of triploids indicates that the hybridization process has a temporal continuity. The lack of observed differences among taxa in age-related life-history aspects indicates that hybrid fitness does not seem to differ from that of the parental species, and reinforce the idea of a potential fertility of hybrids. Besides, our results suggests that hybrids do not direct their resources more to growth than to reproduction, as would be expected if they were infertile. However, further studies are necessary to determine the reproductive capacity of the hybrids.

Evolution of Sex Chromosome Heteromorphy in Geographic Populations of the Japanese Tago’s Brown Frog Complex

The sex chromosomes of most anuran amphibians are characterized by homomorphy in both sexes, and evolution to heteromorphy rarely occurs at the species or geographic population level. Here, we report sex chromosome heteromorphy in geographic populations of the Japanese Tago’s brown frog complex (2n = 26), comprising Rana sakuraii and R. tagoi. The sex chromosomes of R. sakuraii from the populations in western Japan were homomorphic in both sexes, whereas chromosome 7 from the populations in eastern Japan were heteromorphic in males. Chromosome 7 of R. tagoi, which is distributed close to R. sakuraii in eastern Japan, was highly similar in morphology to the Y chromosome of R. sakuraii. Based on this and on mitochondrial gene sequence analysis, we hypothesize that in the R. sakuraii populations from eastern Japan the XY heteromorphic sex chromosome system was established by the introduction of chromosome 7 from R. tagoi via interspecies hybridization. In contrast, chromosome 13 of R. tagoi from the 2 large islands in western Japan, Shikoku and Kyushu, showed a heteromorphic pattern of constitutive heterochromatin distribution in males, while this pattern was homomorphic in females. Our study reveals that sex chromosome heteromorphy evolved independently at the geographic lineage level in this species complex.

Gene flow creates a mirage of cryptic species in a Southeast Asian spotted stream frog complex.

Most new cryptic species are described using conventional tree- and distance-based species delimitation methods (SDMs), which rely on phylogenetic arrangements and measures of genetic divergence. However, although numerous factors such as population structure and gene flow are known to confound phylogenetic inference and species delimitation, the influence of these processes is not frequently evaluated. Using large numbers of exons, introns, and ultraconserved elements obtained using the FrogCap sequence-capture protocol, we compared conventional SDMs with more robust genomic analyses that assess population structure and gene flow to characterize species boundaries in a Southeast Asian frog complex (Pulchrana picturata). Our results showed that gene flow and introgression can produce phylogenetic patterns and levels of divergence that resemble distinct species (up to 10% divergence in mitochondrial DNA). Hybrid populations were inferred as independent (singleton) clades that were highly divergent from adjacent populations (7%-10%) and unusually similar (<3%) to allopatric populations. Such anomalous patterns are not uncommon in Southeast Asian amphibians, which brings into question whether the high levels of cryptic diversity observed in other amphibian groups reflect distinct cryptic species-or, instead, highly admixed and structured metapopulation lineages. Our results also provide an alternative explanation to the conundrum of divergent (sometimes nonsister) sympatric lineages-a pattern that has been celebrated as indicative of true cryptic speciation. Based on these findings, we recommend that species delimitation of continuously distributed "cryptic" groups should not rely solely on conventional SDMs, but should necessarily examine population structure and gene flow to avoid taxonomic inflation.

A reference DNA barcode library for Austrian amphibians and reptiles.

In the last few years, DNA barcoding became an established method for species identification in biodiversity inventories and monitoring studies. Such studies depend on the access to a comprehensive reference data base, covering all relevant taxa. Here we present a comprehensive DNA barcode inventory of all amphibian and reptile species native to Austria, except for the putatively extinct Vipera ursinii rakosiensis and Lissotriton helveticus, which has been only recently reported for the very western edge of Austria. A total of 194 DNA barcodes were generated in the framework of the Austrian Barcode of Life (ABOL) initiative. Species identification via DNA barcodes was successful for most species, except for the hybridogenetic species complex of water frogs (Pelophylax spp.) and the crested newts (Triturus spp.), in areas of sympatry. However, DNA barcoding also proved powerful in detecting deep conspecific lineages, e.g. within Natrix natrix or the wall lizard (Podarcis muralis), resulting in more than one Barcode Index Number (BIN) per species. Moreover, DNA barcodes revealed the presence of Natrix helvetica, which has been elevated to species level only recently, and genetic signatures of the Italian water frog Pelophylax bergeri in Western Austria for the first time. Comparison to previously published DNA barcoding data of European amphibians and reptiles corroborated the results of the Austrian data but also revealed certain peculiarities, underlining the particular strengths and in the case of the genus Pelophylax also the limitations of DNA barcoding. Consequently, DNA barcoding is not only powerful for species identification of all life stages of most Austrian amphibian and reptile species, but also for the detection of new species, the monitoring of gene flow or the presence of alien populations and/or species. Thus, DNA barcoding and the data generated in this study may serve both scientific and national or even transnational conservation purposes.

Sympatric lineages in the Mantidactylus ambreensis complex of Malagasy frogs originated allopatrically rather than by in-situ speciation

Madagascar's biota is characterized by a high degree of microendemism at different taxonomic levels, but how colonization and in-situ speciation contribute to the assembly of local species communities has rarely been studied on this island. Here we analyze the phylogenetic relationships of riparian frogs of the Mantidactylus ambreensis species complex, which is distributed in the north of Madagascar and was originally described from Montagne d’Ambre, an isolated mountain of volcanic origin, currently protected within Montagne d'Ambre National Park (MANP). Data from mitochondrial DNA, and phylogenomic data from FrogCap, a sequence capture method, independently confirm that this species complex is monophyletic within the subgenus Ochthomantis, and identify two main clades within it. These two clades are separated by 5.6–6.8% pairwise distance in the mitochondrial 16S rRNA gene and co-occur in MANP, with one distributed at high elevations (940–1375 m a.s.l.) and the other at lower elevations (535–1010 m a.s.l.), but show almost no haplotype sharing in the nuclear RAG1 gene. This occurrence in syntopy without admixture confirms them as independent evolutionary lineages that merit recognition as separate species, and we here refer to them as high-elevation (HE) and low-elevation (LE) lineage; they will warrant taxonomic assessment to confidently assign the name ambreensis to one or the other. Populations of the M. ambreensis complex from elsewhere in northern Madagascar all belong to the LE lineage, although they do occur over a larger elevational range than in Montagne d'Ambre (285–1040 m a.s.l.). Within LE there are several phylogroups (LE1–LE4) of moderately deep divergence (1.5–2.8% in 16S), but phylogroup LE4 that occurs in MANP has a deeply nested phylogenetic position, as recovered separately by mitochondrial and sequence capture datasets. This suggests that HE and LE did not diverge by a local fission of lower and upper populations, but instead arose through a more complex biogeographic scenario. The branching pattern of phylogroups LE1–LE4 shows a clear south-to-north phylogeographic pattern. We derive from these results a testable hypothesis of vicariant speciation that restricted the HE lineage to MANP and the LE candidate species to a climatic refugium further south, with subsequent northwards range expansion and secondary colonization of MANP by LE. These results provide an example for complex assembly of local microendemic amphibian faunas on Madagascar.

Fossils Reveal Long-Term Continuous and Parallel Innovation in the Sacro-Caudo-Pelvic Complex of the Highly Aquatic Pipid Frogs

Within the already peculiar Bauplan of anurans, pipid frogs have evolved an array of bizarre features that are commonly linked to their highly aquatic lifestyle. Among the latter, there are several distinctive sacro-caudo-pelvic features shared by extant pipids, which have been regarded as evolutionary novelties taking part of a specialized fore-aft-sliding ilio-sacral joint. Pipids and their kin (pipimorphs) have a rich fossil record documenting 130 million years of uninterrupted evolution in aquatic environments, which, along with our current understanding of their phylogeny and recently available musculoskeletal data, allows us to inquire on the patterns and processes that have led to their distinctive sacro-caudo-pelvic system with a deep-time perspective. Here, we take a phylomorphospace approach based on discrete character matrices and a scaffold tree derived from recent studies, making comparisons of morphospace occupation between pipids and other anurans, and morphospace occupation, disparity, levels of homoplasy, and shared evolving characters between different groups and/or over time across pipimorphs. In doing so, we focus on trends of morphological diversification and discuss the potential role that ecological and developmental constraints might have had in driving the evolution of the sacro-caudo-pelvic complex of pipid frogs. Our main findings reveal a pattern of continuous and parallel innovation early in the history of pipids followed by arrested evolution of novel morphologies towards the Recent. The latter, in turn, is mirrored by rampant homoplasy in the ilio-sacral sliding joint among extant pipid frogs. This study highlights the importance of fossils in revealing macroevolutionary patterns that will be otherwise veiled based on neontological data alone.

Combining ultraconserved elements and mtDNA data to uncover lineage diversity in a Mexican highland frog (Sarcohyla; Hylidae).

Molecular studies have uncovered significant diversity in the Mexican Highlands, leading to the description of many new endemic species. DNA approaches to this kind of species discovery have included both mitochondrial DNA (mtDNA) sequencing and multilocus genomic methods. While these marker types have often been pitted against one another, there are benefits to deploying them together, as linked mtDNA data can provide the bridge between uncovering lineages through rigorous multilocus genomic analysis and identifying lineages through comparison to existing mtDNA databases. Here, we apply one class of multilocus genomic marker, ultraconserved elements (UCEs), and linked mtDNA data to a species complex of frogs (Sarcohyla bistincta, Hylidae) found in the Mexican Highlands. We generated data from 1,891 UCEs, which contained 1,742 informative SNPs for S. bistincta and closely related species and captured mitochondrial genomes for most samples. Genetic analyses based on both whole loci and SNPs agree there are six to seven distinct lineages within what is currently described as S. bistincta. Phylogenies from UCEs and mtDNA mostly agreed in their topologies, and the few differences suggested a more complex evolutionary history of the mtDNA marker. Our study demonstrates that the Mexican Highlands still hold substantial undescribed diversity, making their conservation a particularly urgent goal. The Trans-Mexican Volcanic Range stands out as a significant geographic feature in Sarcohyla and may have acted as a dispersal corridor for S. bistincta to spread to the north. Combining multilocus genomic data with linked mtDNA data is a useful approach for identifying potential new species and associating them with already described taxa, which will be especially important in groups with undescribed subadult phenotypes and cryptic species.

Exploring the Developmental Thermal Biology of an Abundant Native Amphibian in Southern California, the Baja California Chorus Frog

The Baja California chorus frog (Pseudacris hypochondriaca), a member of the Pacific chorus frog complex, is probably the most abundant native amphibian in southern California. The persistence of this species when many other amphibians are in decline provides a unique opportunity to examine the developmental and physiological attributes of a successful species. Developing stages are often particularly susceptible to environmental influences, and understanding physiological function during this time can provide insight into the drivers of species abundance and distributions. The focus of our research is to examine how the developmental physiology of the Baja California chorus frog is influenced by, and responds to, temperature. We collected egg clutches from local ponds within 24 h of fertilization. The clutches were separated and incubated at 10°C, 15°C and 20°C. Oxygen consumption rate (Vo2) was measured throughout development at each temperature. Embryos and tadpoles were fixed throughout development in 4% paraformaldehyde in phosphate buffered saline, then transferred to 70% EtOH, removed from their egg (if not already hatched) and photographed under a dissecting microscope. The yolk and embryo/tadpole were separated, weighed, dried at 65°C for 24 h, and reweighed. The stage and length of each embryo/tadpole was determined from photographs. Average time to 50% hatch and hatch window duration was determined across clutches. Development rate was strongly affected by temperature, with warmer temperatures reducing time to hatch. Temperature also influenced the duration of hatching, with the hatch window ranging from a few days at warmer temperatures to over a week at 10°C. Preliminary results indicate Vo2 was higher and more variable in embryos incubated at 20°C, but there was a limited temperature effect on growth, with length, dry mass and yolk dry mass similar between temperatures throughout development. These results indicate the conversion of yolk into tissue occurred at the same rate across temperatures, and the energy allocated to growth was not altered. However, because more oxygen was consumed at 20°C, the cost of development was higher than at 15°C. Individuals incubated in warmer temperatures may be “wasting some oxygen”, but this does not appear to confer negative physiological consequences. We will further explore morphological and physiological responses to temperature in embryos and tadpoles of this species to understand if robust thermal biology contributes to the success of the species.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Invasion genetics of marsh frogs (Pelophylax ridibundus sensu lato) in Switzerland

The marsh frog (Pelophylax ridibundus sensu lato) is the number one amphibian invader in Western Europe. In Switzerland, marsh frogs were introduced in the 1950-1960s and progressively colonized most of the northern parts of the country. We investigated this invasion using molecular tools. We mapped the cryptic presence of three monophyletic mitochondrial lineages (P. ridibundus, P. kurtmuelleri and P. c. f. bedriagae from southeastern Europe) consistent with registered importations by a local frog-leg industry. High nuclear diversity supports that invasive frogs probably originated from genetically-rich import batches and patterns of population differentiation confirm that multiple independent introduction sites were involved. Moreover, several lines of evidence suggest occasional hybridization with local hybridogenetic water frogs. This invasion emphasizes the issues of frequent amphibian releases and translocations at the international and regional scale for commercial and recreational purposes, and stresses for more adequate legislation, control and information to the general public. Given the parallel invasion by alien pool frogs (i. e., the Italian P. bergeri has replaced the local P. lessonae), the situation of water frogs in Switzerland is critical. The water frog complex makes an alarming symbol of the anthropogenic mark left on wildlife diversity and distributions.

Species delimitation with gene flow: A methodological comparison and population genomics approach to elucidate cryptic species boundaries in Malaysian Torrent Frogs.

Accurately delimiting species boundaries is a nontrivial undertaking that can have significant effects on downstream inferences. We compared the efficacy of commonly used species delimitation methods (SDMs) and a population genomics approach based on genomewide single-nucleotide polymorphisms (SNPs) to assess lineage separation in the Malaysian Torrent Frog Complex currently recognized as a single species (Amolops larutensis). First, we used morphological, mitochondrial DNA and genomewide SNPs to identify putative species boundaries by implementing noncoalescent and coalescent-based SDMs (mPTP, iBPP, BFD*). We then tested the validity of putative boundaries by estimating spatiotemporal gene flow (fastsimcoal2, ABBA-BABA) to assess the extent of genetic isolation among putative species. Our results show that the A.larutensis complex runs the gamut of the speciation continuum from highly divergent, genetically isolated lineages (mean Fst =0.9) to differentiating populations involving recent gene flow (mean Fst =0.05; Nm >5). As expected, SDMs were effective at delimiting divergent lineages in the absence of gene flow but overestimated species in the presence of marked population structure and gene flow. However, using a population genomics approach and the concept of species as separately evolving metapopulation lineages as the only necessary property of a species, we were able to objectively elucidate cryptic species boundaries in the presence of past and present gene flow. This study does not discount the utility of SDMs but highlights the danger of violating model assumptions and the importance of carefully considering methods that appropriately fit the diversification history of a particular system.

Methodological approaches for studying the european water frog Pelophylax esculentus complex

The European water frog (Pelophylax esculentus) complex represents a unique and adequate model system for the study of interspecific hybridization and the mechanisms enabling interspecific hybrids to overcome the reproductive barriers. The difficulties in the study of individuals from the P. esculentus complex are associated with high polymorphism of morphological characters in parental species and interspecific hybrids, as well as with the presence of polyploid hybrid forms. From the discovery of the phenomenon of interspecific hybridization and the demonstration of successful reproduction of interspecific hybrids, researchers constantly searched for the methods necessary for the most accurate identification of parental species and various hybrid forms. This review describes biochemical, cytogenetic, and molecular methods and approaches used to identify individuals from the European water frog complex, as well as to analyze the genomes transferred with the gametes of hybrids. The advantages and disadvantages of these approaches are discussed. The presented methods can be used for studying other hybrid complexes of fish, amphibians, and reptiles.