Abstracts (first author)

Talk 

Fragility and robustness – the evolution of tropical intertidal communities as sea level rises and falls

Author(s): Shi S, He Z, Li X, Yang M

Summary:

Sea level changes may strongly impact intertidal communities. In the tropics, their dominant primary producers are the woody plants of mangroves, which are particularly susceptible to such changes. In this study, we surveyed the genetic diversity of 6 mangrove species in the Indo-western Pacific (IWP) region. In all species, the genetic diversity is organized into two regional clades that are separated by the Strait of Malacca. Under repeated freezes (F) and thaws (T) with past glaciations, or the TFT cycle, the two regions experienced phases of isolation and admixture as the Strait opens and closes. The genetic diversity is built up in isolation and shuffled in the admixture phase. Computer simulations of the TFT model show that the historical effective population size in each region is very small, between 200 and 1200. The results support the conjecture of fragile habitats in tropical intertidal zones under rapid sea level changes. Nevertheless, the geographical distributions of haplotypes suggest adaptive complexes being separately built up in the isolation phase, resulting in robust adaptation in the admixture phase and speciation. Hence, the TFT cycle is a double-edged sword that endowed both fragility and robustness on the intertidal communities of IWP. The confluence of several historical factors in the last 5000 years has tilted the balance toward robustness. However, this balance may quickly swing the other way under multiple influences of local human perturbations and global sea level rises.



Abstracts (coauthor)

Summary:

Population genetic analysis of mangroves can reveal their patterns of genetic diversity, which is important for understanding their evolutionary history and scientific conservation. In this study, we examined the nucleotide diversity and population differentiation in six populations of a mangrove tree, Rhizophora apiculata, from China and Thailand based on sequencing 78 nuclear genes through Illumina platform. For each population, more than 30 individuals were pooled for sequencing. The average θw and θπ of the six populations ranged from 0.000263 to 0.000786, and from 0.000258 to 0.000924, respectively, showing low levels of DNA polymorphism within each population. Fst analysis showed strong population structure at the regional level,suggesting Malay Peninsula as a barrier to restrict gene flow between the Andaman Sea and South China Sea despite the existence of the Malacca Strait. However, Fst values vary from zero to one by locus, which could not be explained by simple gene flow model. Haplotype analysis showed two highly divergent haplotypes often reside within populations, which may be caused by recent admixture. Patterns of genetic diversity in this species might result from the repeated glacial events during Plio-Pleistocene, when the Andaman Sea was isolated with South China Sea at the lowered sea level. Reduced genetic diversity in populations from South China Sea can be attributed to lower effective population size for the enormously changed shorelines during this stage. We further used Sanger method to obtain sequences of three genes among 15 populations from wider geographic regions. STRUCTRUE analysis indicated that these populations formed five clusters, corresponding to five geographic regions , which suggests population structure of this species was mainly shaped by geographic isolation. Our study reveals the effect of glacial events on patterns of genetic diversity of an intertidal mangrove tree, which will be informative for its conservation.

Summary:

The evolutionary dynamics of the entire repertoire of microRNAs (miRNAs) has been debated. Disagreements were not resolved partly because new miRNA-like genes emerged constantly but few were evolutionarily or functionally significant. With an extensive search, we identify 12 new adaptive miRNAs that emerged de novo (and often in clusters) in Drosophila melanogaster in the last 4 million years (Myrs). Interestingly, even though they are adaptively evolving at birth, more than 95% of these new miRNAs disappear over time. They serve a useful function, but for only a transient evolutionary period. After 30 Myrs, all surviving miRNAs make the transition from the adaptive phase of rapid evolution to the conservative phase of slow evolution, apparently becoming integrated into the genome. During this transition, the expression shifts from being tissue-specific, predominantly in testes and imaginal discs, to a broader distribution in many other tissues. Unexpectedly, a measurable fraction (20-30%) of these conservatively evolving miRNAs experience "evolutionary reactivation" and begin rapidly evolving again. These reactivated miRNAs start another cycle of adaptive-neutral-conservative evolution that could also lead to death. In conclusion, new adaptive miRNAs go through cycles of evolution, resulting in very slow turnover. Since most new miRNAs evolve adaptively for a transient period of variable length and then disappear, the phenomenon may shed some light on the regulatory roles of miRNAs in general.

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
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