Research Article: Phylogeography in Nassarius mud snails: Complex patterns in congeneric species

Date Published: July 12, 2017

Publisher: Public Library of Science

Author(s): Chuanliang Pu, Haitao Li, Aijia Zhu, Yiyong Chen, Yan Zhao, Aibin Zhan, Tzen-Yuh Chiang.


One major goal for phylogeographical studies is to elucidate respective roles of multiple evolutionary and ecological forces that shape the current distribution patterns. In marine and coastal ecosystems, it has been generated a common realization that species with enormous population size and pelagic larval stages can disperse across broad geographical scales, leading to weak or even no phylogeographical structure across large geographical scales. However, the violation of such realization has been frequently reported, and it remains largely unexplored on mechanisms responsible for various phylogeographical patterns observed in different species at varied geographical scales. Here, we used a species-rich genus Nassarius to assess and compare phylogeographical patterns in congeneric species, and discuss causes and consequences underlying varied phylogeographical patterns. Interestingly, we observed complex phylogeographical patterns both within single species and across multiple species, and multiple analyses showed varied levels of genetic heterogeneity among sites within and across species. Available evidence suggests that related species with similar biological characteristics may not be necessary to result in consistent phylogeographical patterns. Multiple factors, including larval ecology, interactions between dispersal and natural selection, and human activity-mediated dispersal, can partially explain the complex patterns observed in this study. Deep investigations should be performed on these factors, particularly their respective roles in determining evolutionary/ecological processes to form phylogeographical patterns in species with high dispersal capacities in marine and coastal ecosystems.

Partial Text

One of the major goals of phylogeographical analyses is to elucidate relative roles of multiple evolutionary and ecological forces that shape the current distribution patterns of biodiversity [1, 2]. In summary, two major competing forces in the marine realm, that is historical vicariant (isolating) events such as geological barriers versus recent events such as recent gene flow, are commonly used to interpret the phylogeographical patterns and population genetic structure at varied geographical scales [3–6]. Widespread ancestors by vicariant/isolating events lead to disjunct distributions of genetic diversity, while recent gene flow, either by natural processes such as natural dispersal or by human-mediated gene flow, can potentially prevent both reproductive isolation and morphological divergence, resulting in weak phylogeographical patterns and strong genetic homogeneity among isolated populations [2, 3, 7].

In this study, we used both mitochondrial COI and nuclear ITS1 to investigate and compare phylogeographical patterns of Nassarius mud snails along the Chinese coast, particularly in the species-rich regions on the coast of South China Sea. In contrast to the expected “genetic homogenization hypothesis”, we observed complex phylogeographical patterns, with varied levels of genetic heterogeneity within and among species at different geographical scales. Overall, we did not observe the pattern of genetic homogenization even at fine geographical scales where genetic exchanges are expected to facilitate genetic homogenization among sites owing to a long planktonic larval phase (1–2 months for Nassarius species [20]). Multiple analyses showed a high level of genetic heterogeneity at the haplotype/allele, population, and species levels. At the haplotype/allele and population levels, we observed a large proportion of site-specific haplotypes/alleles in populations collected even from fine geographical scales (Table 1; Fig 3). At the species level, the geographical distributions of haplotypes/alleles largely varied among species (Table 1; Fig 3), suggesting that related species with similar biological characteristics may not be necessary to result in consistent phylogeographical patterns. All these results suggest that multiple factors, as well as their complex interactions, are responsible for the observed patterns. Therefore, deep investigations should be performed on species-specific biological features, particularly interactions between species-specific biological features such as larval biology and local environments, and the roles of such interactions in determining phylogeographical patterns and evolutionary/ecological processes in species with high dispersal capacities.




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