4/4/2023 0 Comments Slender salamanderThis has resulted in the establishment on the islands of many non-native invertebrates, these are exemplified by anthropochorus terrestrial isopods of European origin where one to three species are flourishing on each of the islands with the possible exception of Red Rock Island. We note here that since the early days of the European settlement of California, each of the islands in our study region has been impacted by human activities either by mining and/or building operations. The islands have been studied from different perspectives, including detailed geological, botanical and faunistic surveys. The islands of the San Francisco Bay (California, USA) constitute an interesting system from an evolutionary perspective because their origin is relatively recent (Holocene) and thus their study might provide clues to understanding the consequences of population isolation after the interruption of gene flow following the rising of the sea level, especially in a short time scale (the last 9,000 years). Characterization of patterns of gene flow, with the addition of a temporal component, especially in cases when geological information is available allows dating with some precision the amount of time passed since populations have been isolated. The study of colonization patterns and the effects of isolation on divergence may allow identification of potential source populations either from the mainland or other islands in a stepping stone or sweepstake model of colonization. In more recent times, the use of molecular markers has added impetus to the analysis of the complex processes involved in differentiation of island populations. They are often regarded as "natural laboratories" for the study of speciation because geographic isolation promotes morphological, ecological and genetic divergence of newly established populations with respect to their mainland counterparts and thus they offer an excellent opportunity to identify key factors in species formation. Islands have long been the subjects of both theoretical and empirical studies in Evolutionary Biology. g., resulting from founder effects) is similar to that observed in other studies about recent colonization of island habitats. This pattern of rapid morphological divergence (e. In contrast, there is some evidence for rapid morphological changes between populations in some islands and their closest mainland counterparts. It can be said that, based on observed values of genetic diversity, the last 9,000 years of evolution on these islands have been characterized by relative stability, with the occasional extinction of some haplotypes or alleles that were formerly shared between island and mainland populations but overall maintaining high levels of variation (with the exception of Alcatraz). Results of coalescence-based analyses suggest that for most island populations the mtDNA lineages from which they were derived date from the Pleistocene. With the two noted exceptions, it is clear that most island populations were established prior to the 9,000 years since the formation of the Bay. attenuatus in the San Francisco Bay Area and its islands. In spite of marked differences between the evolutionary rates of the two kinds of molecular markers, both indicate distinctive and similar patterns of population structure for B. There are two exceptions (Alcatraz and Yerba Buena) where the evidence suggests that salamander populations are wholly or in part, the result of anthropogenic introductions.Ĭomparison of the molecular data and the interpretations drawn therefrom with an earlier morphological study of many of the same salamander populations show some of the same evolutionary trends. There was a high degree of congruence in the results of analyses of nucleotide and allozyme data, both of which strongly support the hypothesis that, for the majority of the islands, salamanders are descended from hilltop populations that became isolated with the formation of the Bay ca. In this study, molecular markers of mitochondrial and nuclear derivation were used to investigate the evolution, structure and origin of populations of the California slender salamander ( Batrachoseps attenuatus) inhabiting the six major islands of San Francisco Bay, formed following the rising of sea level around 9,000 years ago. Island populations are excellent model systems for studies of phenotypic, ecological and molecular evolution.
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