Intraspecific relationships among the stygobitic shrimp Typhlatya mitchelli, by analyzing sequence data from mitochondrial DNA

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Title: Intraspecific relationships among the stygobitic shrimp Typhlatya mitchelli, by analyzing sequence data from mitochondrial DNA
Author: Webb, Michael Scott
Abstract: Intraspecific relationships among the anchialine cave shrimp Typhlatya mitchelli were examined by sequencing a total of 1505 bp from portions of three mitochondrial DNA genes . Cytochrome b , cytochrome oxidase I , and 16S rRNA were partially sequenced and analyzed for specimens from six different cenotes (water -filled caves ) across the Yucatan Peninsula , Mexico . The conspecific Typhlatya pearsei that is sympatric with T . mitchelli was also sequenced and used as the outgroup . Comparisons among specimens of T . mitchelli yielded low sequence divergence values (0 -1 .7 % ) , with the majority being less than 0 .4 % . Phylogenetic tree topologies reconstructed with neighbor -joining , maximum likelihood , and maximum parsimony were in agreement in regards of the resolution of deep branches . Also , there was no obvious geographic differentiation among the majority of T . mitchelli samples , with the exception of specimens from Cenote San Antonio Chiich (Yokdzonot , Yucatan , Mexico ) which all clustered into an extremely well supported monophyletic group . The level of differentiation of this group , together with the nearly total absence of differentiation among T . mitchelli from distant cave systems , suggests that this is an Evolutionary Significant Unit (ESU ) , which may correspond to a new species . This unidentified Typhlatya from Cenote San Antonio Chiich was helpful in establishing a period in which the epigean ancestor colonized the cenotes . Based on pairwise distance data and previously published shrimp molecular clocks (Baldwin et al . , 1998 ) , T . mitchelli and the putative new Typhlatya species last shared a common ancestor between 3 -5 million years ago (mya ) , during the mid -Pliocene era , while T . mitchelli and T . pearsei was approximately 7 -10 mya (middle to late Miocene ) . The ancestor to T . mitchelli and the unidentified Typhlatya species abandoned its shallow coastal water existence in the early Pliocene and eventually expanded its range across the peninsula . Approximately 4 mya , Cenote San Antonio Chiich became isolated from the remaining gene pool thereby halting gene flow . As the regional water table fluctuated in response to the rise and fall of Pleistocene sea levels , T . mitchelli actively colonized the peninsula . The discovery of a single , continuous subterranean freshwater system provides for a better understanding of anchialine biogeography within the Yucatan Peninsula .
URI: http : / /hdl .handle .net /1969 .1 /14
Date: 2004-09-30

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Intraspecific relationships among the stygobitic shrimp Typhlatya mitchelli, by analyzing sequence data from mitochondrial DNA. Available electronically from http : / /hdl .handle .net /1969 .1 /14 .

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