Genetic diversity and connectivity remain high in Holothuria polii (Delle Chiaje 1823) across a coastal lagoon-open sea environmental gradient

Abstract

Coastal lagoons represent habitats with widely heterogeneous environmental conditions, particularly as regards salinity and temperature, which fluctuate in both space and time. These characteristics suggest that physical and ecological factors could contribute to the genetic divergence among populations occurring in coastal lagoon and open-coast environments. This study investigates the genetic structure of Holothuria polii at a micro-geographic scale across the Mar Menor coastal lagoon and nearby marine areas, estimating the mitochondrial DNA variation in two gene fragments, cytochrome oxidase I (COI) and 16S rRNA (16S). Dataset of mitochondrial sequences was also used to test the influence of environmental differences between coastal lagoon and marine waters on population genetic structure. All sampled locations exhibited high levels of haplotype diversity and low values of nucleotide diversity. Both genes showed contrasting signals of genetic differentiation (non-significant differences using COI and slight differences using 16S, which could due to different mutation rates or to differential number of exclusive haplotypes. We detected an excess of recent mutations and exclusive haplotypes, which can be generated as a result of population growth. However, selective processes can be also acting on the gene markers used; highly significant generalized additive models have been obtained considering genetic data from 16S gene and independent variables such as temperature and salinity.

Environmental variables, habitat discontinuity and life history shaping the genetic structure of Pomatoschistus marmoratus

“…As P. marmoratus is associated with brackish and hyper-saline habitats, which are systems suffering frequent environmental fluctuations and disturbances, this species could have been exposed to extreme conditions more frequently than other marine species inhabiting open sea habitats. Our results point a significant link between extreme lagoonal environmental conditions (mainly maximum salinity) and genetic composition, such as it was already demonstrated on cockles and sea cucumbers populations from the Mar Menor lagoon (González-Wangüemert et al 2009;Vergara-Chen et al 2010b). This find is very interesting because previously several authors had defined different ecological requirements for the various Pomatochistus species; for example, P. marmoratus survives to higher salinities than P. microps, especially in habitats whose temperature and salinity change through the year, but do not vary abruptly (Berrebi et al 2005).…”

“…On the other hand, the lack of significance in the AMOVA comparisons between groups could be also due to low power associate with a low number of populations per group such as was described by Fitzpatrick (2009). Therefore, according to our results from F ST values, Cavalli-Sforza genetic distances, correspondence analysis and significant genic and genotypic differentiation, we suggested that the highest genetic divergence observed between samples (Mazarrón and the rest of localities) could be consequence of the isolation of lagoonal populations from open sea which has been already reported in other coastal fishes such as Pomatoschistus minutus Berrebi et al 2009), Dicentrarchus labrax (Lemaire et al 2000), Atherina lagunae (Trabelsi et al 2004), Atherina boyeri (Kraitsek et al 2008;Milana et al 2012), Diplodus sargus (González-Wangüemert and Pérez-Ruzafa 2012) and several invertebrate species (Camilli et al 2001;González-Wangüemert et al 2006;Tarnowska et al 2010;Vergara-Chen et al 2010b).…”

“…GAMs represent the relationship between the response variable and the predictors by smooth functions, which can take virtually any form (Hastie and Tibshirani 1990). These models have been applied on genetic and environmental data previously (Snäll et al 2004;Parisod and Bonvin 2008;González-Wangüemert et al 2009;Vergara-Chen et al 2010b). The GAMs were evaluated by examining the proportion of explained deviance and minimizing the generalized cross-validation (GCV; Wood 2000; Wood and Augustin 2002) and the Akaike information criterion (AIC; Venables and Ripley 2004) scores.…”

Effects of fishery protection on biometry and genetic structure of two target sea cucumber species from the Mediterranean Sea

“…The high number of exclusive haplotypes showed in Kusadasi area may increase their fitness under unusual conditions (Ryman et al, 1995;Pérez-Ruzafa et al, 2006;Vergara-Chen et al, 2010;González-Wangüemert & Vergara-Chen, 2014). That genetic diversity could provide the raw material for the maintenance of the diversity longer evolutionary time-scales and may also confer the basis for adaptation to environmental change (Sanford & Kelly, 2011;González-Wangüemert & Vergara-Chen, 2014).…”

“…According previous genetic studies carried out on sea cucumbers (Vergara-Chen et al, 2010;Borrero-Pérez et al, 2011;González-Wangüemert & Borrero-Pérez, 2012;Valente et al, 2014), a representative number of individuals from each locality were analyzed. DNA extractions were done based on Sambrook et al (1989) protocol.…”