Gynogenetic diploids, tetraploids, or octoploids, and a path to polyploidy in Anuran Amphibians

Unreduced gametes have been implicated in the evolution of polyploid species of plants and animals and are normally produced by female anuran amphibians. Such eggs may initiate the evolution of polyploid species that have independently arisen in several anuran families. Polyploid females could also produce unreduced eggs that might lead to species with higher ploidy levels or their eggs may develop gynogenetically to reduce the ploidy level. Diploid Hyla chrysoscelis (2n=24) and tetraploid H. versicolor (4n=48) are sibling cryptic species of North American Grey Treefrogs. Artificial crosses using H. versicolor females and genetically distant diploid males were performed to produce haploid H. versicolor and to assess the production of unreduced eggs in this tetraploid species. Gynogenetic diploid (haploid H. versicolor), allotriploid, gynogenetic tetraploid, allopentaploid, autohexaploid, and gynogenetic octoploid tadpoles were confirmed using chromosome counts from tadpole tail tip squashes. Transformation and survival of the different ploidies varied. Gynogenetic diploids transformed but expressed aspects of the haploid syndrome and died before or shortly after transformation.

Predator-specific responses and emergent multi-predator effects on oviposition site choice in grey treefrogs, Hyla chrysoscelis

Predators affect prey through both consumptive and non-consumptive effects (NCEs), and prey typically face threats from multiple simultaneous predators. While different predators have a variety of NCEs on prey, little is known regarding effects of simultaneous multiple predators on demographic habitat selection. Demographic habitat selection is unique among NCEs, especially in discrete habitat patches; decisions directly affect both distribution and abundance of species across habitat patches, rather than simply abundance and performance within patches. Our goal was to determine strength of avoidance responses to multiple species/species combinations of predatory fish, and responses to predator richness. We assessed responses of ovipositing grey treefrogs ( Hyla chrysoscelis ) to three predatory fish species and substitutive combination of species. In single-species treatments, treefrogs avoided only one species, Notemigonus crysoleucas . All two-species combinations, and the three-species combination, were avoided, including the Fundulus chrysotus × Noturus phaeus combination, of which neither were avoided alone. This suggests emergent properties of multiple predators, with potential interactive effects among cues themselves or in the perception of cues by treefrogs. Our results indicate effects of multiple predators are not predictable based on individual effects, and illustrate the importance and complexity of effects of demographic habitat selection on distribution and abundance.

Revisiting the evolution of the North American tetraploid treefrog (Hyla versicolor)

Hyla chrysoscelis and H. versicolor are common treefrogs in eastern North America and are a cryptic diploid–tetraploid species pair. They are morphologically identical but H. versicolor is a tetraploid. They can be identified acoustically by the male’s advertisement mating call, which has a pulse repetition rate that has twice as many pulses per second in the diploid species, H. chrysoscelis. We used isozymes, microsatellite DNA alleles, and mitochondrial cytochrome b sequences to test the hypothesis that gene exchange occurs between the diploid and tetraploid species in sympatric populations. Each method provided results that are best explained by occasional hybridization of female H. versicolor and male H. chrysoscelis. We propose that H. versicolor first arose from an autotriploid H. chrysoscelis female that produced unreduced triploid eggs. After H. versicolor became established, genes could be passed from H. chrysoscelis to H. versicolor in sympatric populations when these species hybridize. Their F1 female progeny produce unreduced triploid eggs that are fertilized by haploid H. chrysoscelis sperm to reconstitute H. versicolor. Genes can be passed from diploid H. chrysoscelis to tetraploid H. versicolor in sympatric populations.