Formation Of Reproductive Isolation Research Articles

Clusters of Repetitive DNA Sequences in Chromosomes of Voles of the Subgenus Microtus (Microtus, Arvicolidae)

The study is focused on the analysis of the mechanisms underlying the formation and distribution of repeat clusters in mammalian chromosomes, as exemplified by a group of closely related species of voles of the subgenus Microtus (Microtus, Arvicolini). The distribution of repetitive sequences that are the parts of de novo formed heterochromatic regions of Microtus arvalis in two chromosomal forms of this species and three closely related species, M. rossiaemeridionalis, M. kirgisorum, and M. transcaspicus, was analyzed in detail. Possible relationships between the introduction of repetitive sequences, their transpositions, amplification, and the formation of reproductive isolation, which can lead to speciation, are discussed.

THE PECULIARITIES OF CARIOTYPIC EVOLUTION OF MAMMALIS IN THE CAUCASUS MOUNTAINS

Резюме. В настоящей работе изучен хромосомный полиморфизм на основе анализа кариотипов более100 видов и внутривидовых форм Mammalia Кавказа. Порядок дивергенции ветвей на филогенетических древах, полученных по разным хромосомным перестройкам, неоднозначен, что, возможно, есть следствие недавнего и быстрого отделения от основного ствола ряда групп. Впервые отмечено, что морфологическая эволюция не всегда сопровождалась видимыми хромосомными перестройками и наоборот. Полученные данные свидетельствуют в пользу хромосомного видообразования в ряде родов: Talpa, Sicista, Pitymys, Microtus и т.д.

Dobzhansky’s rule and reinforcement of prezygotic reproductive isolation in zones of secondary contact

It is well known that closely related sympatric species are usually more different in characters involved in species recognition (e.g., in visual and acoustic signals) than allopatric species of the same evolutionary age. In this article I call this phenomenon Dobzhansky's rule in accordance with the name of the scientist who first discovered it. There are two alternative explanations for this pattern. Under hypothesis of reinforcement by Dobzhansky, these species-specific differences evolve in situ, exactly in zone of overlap between two populations. Under hypothesis of differential fusion by Templeton, the differences originate in geographically separated regions, and only those populations that have evolved such differences can persist in secondary sympatry. These evolutionary scenarios are significantly different. The scenario by Dobzhansky is an essentially sympatric model, in which natural selection reinforces pre-zygotic isolation between divergent populations by selecting against unfit hybrids. The scenario by Templeton is based on classic allopatric speciation model that consider the formation of reproductive isolation to be a by-product of divergent evolution. In this work we show that the sympatric distribution of sister taxa of Agrodiaetus butterflies strongly correlates with differences in male wing colour. We also use a new quantitative phylogenetic test to distinguish between the models by Dobzhansky and by Templeton and to demonstrate that the pattern observed is, most likely, the result of reinforcement.

Phylogeny and phylogeography of the sword-tailed newt, Cynops ensicauda (Amphibia: Caudata), as revealed by nucleotide sequences of mitochondrial DNA

We investigated the phylogenetic relationships and phylogeography among individuals of the endemic newt (Cynops ensicauda) of the Central Ryukyus, Japan based on the mitochondrial cytochrome b gene. The results of phylogenetic analyses showed the presence of remarkable differentiation between assemblages from the Amami and Okinawa Island Groups, supporting the validity of the subspecies C. e. popei described from the latter on morphological grounds. The group of individuals from Okinawa Island Group was further divided into two distinct subgroups unlike the results of previous morphological and allozyme studies. Geographic ranges of these subgroups overlapped in the northern part of Okinawajima Island. The phylogeographic pattern within the Okinawa Island Group suggests an initial division into two geographically isolated population lineages and subsequent secondary sympatry before formation of reproductive isolation. It is also likely that within the Okinawa Island Group emigration occurred from the central and northern parts of Okinawajima Island to its southern part, as well as to several small islets off its western coast. Within the Amami Island Group, recurring restricted gene flow with isolation by distance seems to have occurred around the southwestern region including three islets southwest of Amamioshima Island.

The development of an artificial hybrid and revealing elements of reproductive isolation between sympatric forms of Dryagin’s char and Salvelinus alpinus complex (Salmonidae) from Sobachye Mountain Lake (Taimyr)

The embryonic-larval development (at 3°C) of a hybrid between sympatric lake forms of Arctic char Salvelinus alpinus complex (large females of Dryagin’s char x male goggle-eyed char) from the polar mountain Lake Sobachye (the Norilo-Pyasina water system, Taimyr) was studied. No morphological disturbances were found in the embryonic membrane during development. After hatching, because of yolk sac soaking and blood circulation disturbances along its vessels, about 15% of specimens perished. The most mass disturbances in the development of free embryos and larvae that were manifested in the body curvature, loss of mobility, and subsequent death of a greater proportion of specimens were caused by modifications of differentiation of mesenchymal cells responsible for the axial skeleton formation. It is suggested that anomalies in osteogenesis and a high variation of age when dermal cranial bones (praeoperculum and frontale) appear that bear seismosensory system canal are related to the conflict of genetic programs of the development of parental forms. The rate of embryonic larval development of hybrid specimens exceeds that in the lake small form of Arctic char from Lake Davatchan (Transbaikalia) reared under the same conditions. The reproductive isolation of sympatric Dryagin’s char and goggle-eyed char in Lake Sobachye is provided by both pre- and postcopulation mechanisms. A possible mechanism of formation of reproductive isolation of sympatric forms related to colonization by them of a deep-water biotope is discussed.

Extreme mtDNA divergences in a terrestrial slug (Gastropoda, Pulmonata, Arionidae): accelerated evolution, allopatric divergence and secondary contact

Extremely high levels of intraspecific mtDNA differences in pulmonate gastropods have been reported repeatedly and several hypotheses to explain them have been postulated. We studied the phylogeny and phylogeography of 51 populations (n = 843) of the highly polymorphic terrestrial slug Arion subfuscus (Draparnaud, 1805) across its native distribution range in Western Europe. By combining the analysis of single stranded conformation polymorphisms (SSCP) and nucleotide sequencing, we obtained individual sequence data for a fragment of the mitochondrial 16S rDNA and a fragment of the nuclear ITS1. Additionally, five polymorphic allozyme loci were scored. Based on the 16S rDNA phylogeny, five monophyletic haplotype groups with sequence divergences of 9-21% were found. Despite this deep mitochondrial divergence, the haplotype groups were not monophyletic for the nuclear ITS1 fragment and haplotype group-specific allozyme alleles were not found. Although there is evidence for an accelerated mtDNA clock, the divergence among the haplotype groups is older than the Pleistocene and their current allopatric ranges probably reflect allopatric divergence and glacial survival in separate refugia from which different post-glacial colonization routes were established. A range-overlap of two mtDNA groups (S1 and S2, 21% sequence divergence) stretched from Central France and Belgium up to the North of the British Isles. The nuclear data suggest that this secondary contact resulted in hybridization between the allopatrically diverged groups. Therefore, it seems that, at least for two of the groups, the deep mtDNA divergence was only partially accompanied by the formation of reproductive isolation.

Chromosomal and genic mechanisms of reproductive isolation: the case of Suncus murinus

In this paper we review the results of our studies on the relative contribution of chromosomal and genic divergence in the formation of reproductive isolation in the house musk shrew Suncus murinus (Linnaeus, 1766).

Expression of annexin during spermatogenesis in the newt, cynops pyrrhogaster

We investigated the phylogenetic relationships and phylogeography among individuals of the endemic newt (Cynops ensicauda) of the Central Ryukyus, Japan based on the mitochondrial cytochrome b gene. The results of phylogenetic analyses showed the presence of remarkable differentiation between assemblages from the Amami and Okinawa Island Groups, supporting the validity of the subspecies C. e. popei described from the latter on morphological grounds. The group of individuals from Okinawa Island Group was further divided into two distinct subgroups unlike the results of previous morphological and allozyme studies. Geographic ranges of these subgroups overlapped in the northern part of Okinawajima Island. The phylogeographic pattern within the Okinawa Island Group suggests an initial division into two geographically isolated population lineages and subsequent secondary sympatry before formation of reproductive isolation. It is also likely that within the Okinawa Island Group emigration occurred from the central and northern parts of Okinawajima Island to its southern part, as well as to several small islets off its western coast. Within the Amami Island Group, recurring restricted gene flow with isolation by distance seems to have occurred around the southwestern region including three islets southwest of Amamioshima Island.

BEHAVIORAL REPRODUCTIVE ISOLATION AMONG POPULATIONS OF THE ROTIFER BRACHIONUS PLICATILIS.

Several theories have been proposed to explain how reproductive isolation develops between populations (see Mayr, 1970; Bush, 1975; Carson, 1975; Templeton, 1980, 1981). Different mechanisms have been suggested for allopatric, sympatric, and parapatric populations, and there is some consensus about the importance of geographical isolation. Considerable disagreement persists, however, concerning the role of selection and genetic drift in the formation of reproductive isolation, as well as whether pre-mating or post-mating barriers develop first. Muller (1942) was the first to argue that reproductive barriers appear as by-products of adaptations to different environments. Populations adapting to different environments accumulate genetic differences that eventually lead to reproductive isolation. Dobzhansky (1940) placed more emphasis on the role of natural selection in the formation of barriers to gene flow. He supposed that slight post-mating barriers appear in allopatric populations, but that pre-mating barriers arise when the two populations come into contact once again. At this time selection against hybrids produces the preponderance of reproductive isolation between the incipient species. Carson (1968, 1971) has emphasized the role of genetic drift through founder effects in the formation of reproductive isolation between populations with his population flush principle. While there is still disagreement about the evolutionary dynamics of how reproductive isolation develops, the existence of reproductive isolation in many groups is well documented. Numerous examples of both preand post-mating reproductive isolating mechanisms can be found in any modern textbook on evolutionary biology. Furthermore, it is generally agreed that behavioral reproductive isolation plays a premier role in animal speciation (Dobzhansky, 1970). In certain groups, the type of reproductive isolating mechanisms that operate and how they develop is still largely unknown. This is true of zooplankton in general and rotifers in particular. For rotifers, ecologists and systematists have provided some initial insights into how pre-mating mechanisms might contribute to reproductive isolation. Allopatry probably plays a major role, at least in fresh water rotifers, because of the patchy nature of lake environments. This discrete type of environment is likely to pose substantial barriers to gene flow between populations inhabiting different lakes. Temporal isolation among populations also appears to be important. In the cyclical parthenogenetic breeding system of rotifers (Birky and Gilbert, 1971; King and Snell, 1977), sexual reproduction is an ephemeral event. Observations in natural populations suggest that rotifer species which co-occur in a habitat, often do not overlap in their periods of sexual reproduction (WesenbergLund, 1930; Carlin, 1943; reviewed by King, 1980). This lack of temporal correspondence in sexual periods could be an effective reproductive isolating mechanism. Only a single work (Gilbert, 1963) has provided any detail about the operation of behavioral reproductive isolating mechanisms in rotifers. In reciprocal tests using the freshwater rotifers Brachionus calycifiorus and Brachionus angularis, Gilbert found the males of both of these species completely species-specific in their mating reactions. When B. calycifiorus males were tested with females of three additional ro-