Cryptic habitats and cryptic diversity: unexpected patterns of connectivity and phylogeographical breaks in a Mediterranean endemic marine cave mysid

Abstract

The marine cave‐dwelling mysid Hemimysis margalefi is distributed over the whole Mediterranean Sea, which contrasts with the poor dispersal capabilities of this brooding species. In addition, underwater marine caves are a highly fragmented habitat which further promotes strong genetic structuring, therefore providing highly informative data on the levels of marine population connectivity across biogeographical regions. This study investigates how habitat and geography have shaped the connectivity network of this poor disperser over the entire Mediterranean Sea through the use of several mitochondrial and nuclear markers. Five deeply divergent lineages were observed among H. margalefi populations resulting from deep phylogeographical breaks, some dating back to the Oligo‐Miocene. Whether looking at the intralineage or interlineage levels, H. margalefi populations present a high genetic diversity and population structuring. This study suggests that the five distinct lineages observed in H. margalefi actually correspond to as many separate cryptic taxa. The nominal species, H. margalefi sensu stricto, corresponds to the westernmost lineage here surveyed from the Alboran Sea to southeastern Italy. Typical genetic breaks such as the Almeria‐Oran Front or the Siculo‐Tunisian Strait do not appear to be influential on the studied loci in H. margalefi sensu stricto. Instead, population structuring appears more complex and subtle than usually found for model species with a pelagic dispersal phase. The remaining four cryptic taxa are all found in the eastern basin, but incomplete lineage sorting is suspected and speciation might still be in process. Present‐day population structure of the different H. margalefi cryptic species appears to result from past vicariance events started in the Oligo‐Miocene and maintained by present‐day coastal topography, water circulation and habitat fragmentation.

Census of biodiversity in marine caves of the eastern Mediterranean Sea

“…Marine caves constitute fragmented habitats (Harmelin et al, 1985), especially in the eastern Mediterranean, an area presenting heterogeneity in abiotic conditions, seascape, and coastline geomorphology. These features may function as phylogeographic breaks, influencing isolation and triggering speciation processes, as shown by Rastorgueff et al (2014). The vast majority of marine caves recorded in the Aegean ecoregion are located in insular areas (Giakoumi et al, 2013), possibly indicating a higher level of isolation (Bibiloni et al, 1989).…”

“…Bailey, 1969;Hayward, 1974; ranean areas and showed that sponges exhibit clear biogeographic patterns, thus underlining the need to conserve this habitat across the Mediterranean in order to ensure representativeness. Rastorgueff et al (2014) studied cave mysid populations throughout the northern Mediterranean and revealed contrasting patterns of genetic structuring between the western and eastern parts of the basin, which could be attributed to the presence of phylogeographic breaks. Spatial heterogeneity among and within ecoregions is considered a crucial factor that needs to be taken into account in future conservation plans (Giakoumi et al, 2013).…”

Niche differentiation, habitat fragmentation and population connectivity implications in Mediterranean marine cave-dwelling mysids

“…1a & b) forms mobile swarms above the sediment that number several hundreds of thousands of individuals ( Fig. 1a; Rastorgueff et al 2014). It reaches the entrance of caves at night to feed mostly on phytoplankton-derived material inside and outside the bottom of caves (Rastorgueff et al 2011).…”

“…H. mariannae therefore appears to experience a more fragmented habitat than H. margalefi. Phylogeographic studies have revealed the strong population genetic structure of H. margalefi and have shown a remarkable connectivity between populations of H. mariannae, even at the scale of the Mediterranean Sea Rastorgueff et al 2014), which is attributed to the differences in their ability to use cavities as habitats. Since H. margalefi forms large swarms, it can only be found in large caves.…”

Análises estatísticas de Cloudina spp. no sul da faixa Paraguai e Namíbia. E suas implicações filogenéticas e evolutivas.

“…Os resultados da tabela 10 representam os valores obtidos para diversas mensurações em cada estrutura encontrada. Trabalhos atuais têm demonstrado que espécies descritas como generalistas (com alta plasticidade fenotípica) ampla distribuição geográfica possuem claras evidências de se tratarem de espécies crípticas (Zhou et al, 2012;Rastorgueff et al, 2014;Chen et al, 2017) morfologicamente semelhantes, apenas análises moleculares (filogenia mitocondrial) têm tornado possível a separação destes táxons e demonstrado que barreiras geográficas e instabilidade climática têm um papel importante na especiação destes grupos. O final do Ediacarano foi marcado por eventos geofísicos intensos como os descritos na introdução.…”