Extraordinarily rapid life-history divergence between Cryptasterina sea star species

Abstract

Life history plays a critical role in governing microevolutionary processes such as gene flow and adaptation, as well as macroevolutionary processes such speciation. Here, we use multilocus phylogeographic analyses to examine a speciation event involving spectacular life-history differences between sister species of sea stars. Cryptasterina hystera has evolved a suite of derived life-history traits (including internal self-fertilization and brood protection) that differ from its sister species Cryptasterina pentagona, a gonochoric broadcast spawner. We show that these species have only been reproductively isolated for approximately 6000 years (95% highest posterior density of 905-22 628), and that this life-history change may be responsible for dramatic genetic consequences, including low nucleotide diversity, zero heterozygosity and no gene flow. The rapid divergence of these species rules out some mechanisms of isolation such as adaptation to microhabitats in sympatry, or slow divergence by genetic drift during prolonged isolation. We hypothesize that the large phenotypic differences between species relative to the short divergence time suggests that the lifehistory differences observed may be direct responses to disruptive selection between populations. We speculate that local environmental or demographic differences at the southern range margin are possible mechanisms of selection driving one of the fastest known marine speciation events.

Phylogeography unplugged: comparative surveys in the genomic era

“…The mode and scale of dispersal are known to have a broad impact on genetic structuring, speciation, and resulting diversity pattern (Paulay andMeyer 2006, Malay andPaulay 2009). Egg size, mode of development, and pelagic period can evolve rapidly and often differ among closely related species (Schulze et al 2000, Collin 2004, Marko and Moran 2002, Puritz et al 2012b. Aside from these ecological effects, the large effective population sizes of most marine species may obscure events such as recent speciation and range expansion, due to non-equilibrium allele frequencies, incomplete lineage sorting, and non-concordant patterns among loci.…”

Shallow gene pools in the high intertidal: extreme loss of genetic diversity in viviparous sea stars ( Parvulastra )

“…In the sea star family Asterinidae (cushion stars), four lineages in three genera have evolved self-fertilization, internal brood protection of larvae and live birth of benthic juveniles (figure 1) [14]. We showed that extreme inbreeding and loss of genetic diversity in a live-bearing self-fertile hermaphrodite (Cryptasterina hystera) has evolved on a time scale of a few thousand years (since its divergence from Cryptasterina pentagona), similar to the temporal scale associated with ecological variables in conservation genetics studies [15]. Here, we extend this comparison [16] to two additional species of self-fertile livebearing asterinids: the sister species Parvulastra parvivipara and Parvulastra vivipara.…”

“…25 km) (table 1). We characterized allele-size variation at seven microsatellite loci [19,21], and nucleotide sequence variation in a nuclear intron (glucose-6-phosphate isomerase or GPI) [15,21] (GenBank accessions no. KC866341-42) and two parts of the mitochondrial genome concatenated together as a single locus (several transfer RNA genes plus the control region) [21,22] (KC876801-859).…”

“…We used standard frequency-based population genetic methods to characterize diversity within populations and differentiation between pairs of populations for each species [15,21]. We fitted isolation-with-migration models to data from polymorphic loci for pairs of populations in each species (table 1) using IMa [23] (see the electronic supplementary material).…”

Spore Germination Determines Yeast Inbreeding according to Fitness in the Local Environment

“…In plants, genetic differentiation among populations is greater for selfing species than for outcrossing species (Hamrick and Godt 1996), and selfing is thought to promote speciation by increasing reproductive isolation between sympatric populations, both in plants (Wendt et al 2002;Martin and Willis 2007) and in animals (Puritz et al 2012). Although genetic differentiation may occur as an unselected side effect of selfing, selfing can be directly selected because it reinforces reproductive isolation (e.g., Fishman and Wyatt 1999).…”