Hybridization and polyploidy play an important role in animal speciation. European water frogs of the Pelophylax esculentus complex demonstrate unusual genetic phenomena associated with hybridization, clonality and polyploidy which presumably indicate an initial stage of reticulate speciation. The Seversky Donets River drainage in north-eastern Ukraine is inhabited by both sexes of the diploid and triploid hybrid P. esculentus and only one parental species Pelophylax ridibundus. Based on the presence of various types of hybrids, all populations studied can be divided into three geographical groups: I) P. ridibundus-P. esculentus without triploids; II) P. ridibundus-P. esculentus without diploid hybrids; and III) P. ridibundus-P. esculentus with a mixture of diploids and triploids. A study of gametogenesis revealed that diploid P. esculentus in populations of the first type usually produced haploid gametes of P. ridibundus and a mixture of haploid gametes that carried one or another parental genome (hybrid amphispermy). In populations of the second type, hybrids are derived from crosses of P. ridibundus males with triploid hybrid females producing haploid eggs with a genome of P. lessonae. Therefore, we suggest that clonal genome duplication in these eggs might be the result of suppression of second polar body formation or extra precleavage endoreduplication. In populations of the third type, some diploid females can produce diploid gametes. Fertilization of these eggs with haploid sperm can result in triploid hybrids. Other hybrids here produce haploid gametes with one or another parental genome or their mixture giving rise to new diploid hybrids.
We studied the distribution of Palearctic green toads (Bufo viridis subgroup), an anuran species group with three ploidy levels, inhabiting the Central Asian Amudarya River drainage. Various approaches (one-way, multivariate, components variance analyses and maximum entropy modelling) were used to estimate the effect of altitude, precipitation, temperature and land vegetation covers on the distribution of toads. It is usually assumed that polyploid species occur in regions with harsher climatic conditions (higher latitudes, elevations, etc.), but for the green toads complex, we revealed a more intricate situation. The diploid species (Bufo shaartusiensis and Bufo turanensis) inhabit the arid lowlands (from 44 to 789 m a.s.l.), while tetraploid Bufo pewzowi were recorded in mountainous regions (340-3492 m a.s.l.) with usually lower temperatures and higher precipitation rates than in the region inhabited by diploid species. The triploid species Bufo baturae was found in the Pamirs (Tajikistan) at the highest altitudes (2503-3859 m a.s.l.) under the harshest climatic conditions.
Рассмотрена проблема полиплоидии у амфибий. Ныне известны 53 полиплоидных вида из 15 родов и 10 семейств. Все они встречаются только среди бесхвостых амфибий. Эти виды можно распределить по 4 группам с разным уровнем плоидности: I (триплоиды)-4 вида Bufotes, II (тетраплоиды)-33 вида из 14 родов и 10 семейств, III (октоплоиды)-12 видов из 3 родов и 3 семейств и IV (додекаплоиды)-4 вида из рода Xenopus. Известен лишь один таксон надвидового уровня (подрод Xenopus), полностью состоящий из полиплоидных видов (от 4n до 12n). Среди амфибий насчитывается не менее 10 диплоидно-полиплоидных комплексов. В природе триплоидные особи могут возникать в зоне гибридизации ди-и тетраплоидных видов, а также с невысокой встречаемостью в пределах диплоидных видов. Кроме того, полиплоидные особи (от 3n до 5n) обычны среди диплоидно-полиплоидных гибридогенных форм, размножение которых происходит за счет различных типов клонального наследования (Ambystoma и Pelophylax). Концепция сетчатого (гибридогенного) видообразования, связанная с межвидовой гибридизацией, клональным наследованием и полиплоидией, подтверждается для амфибий в свете новых данных. Полиплоидные виды амфибий значительно чаще встречаются в южных регионах земного шара, чем на севере. В Ориентальной области полиплоиды практически отсутствуют. Библиогр. 39 назв. Ил. 1. Табл. 2. Ключевые слова: амфибии, гибридизация, полиплоидия, сетчатое видообразование.
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