Population Genomics to assess the health and resilience of deep-water crustaceans
Leveraging the power of the reduced representation library method, ddRADseq, we undertook a series of population genomic studies focused on marine invertebrates. We targeted six species of midwater invertebrate common to the mesopelagic Gulf of Mexico, including three crustacean species and three cephalopod species. This work culminated in two comparative studies, both of which revealed high genetic connectivity between the Gulf and the greater Atlantic. In both studies, however, one of the three species was found to exhibit some population differentiation. The Vampire Squid appeared to exist in two populations, though both were present in the Gulf and the greater Atlantic (that is, population differentiation was not basin-specific). We hypothesize that differentiation may be occurring along a depth gradient, driven by dissolved oxygen availability. Population differentiation was also discovered in one species of midwater crustacean, Robustosergia robusta, which had a Gulf population distinct from the Atlantic population. We hypothesized this may be due to the diel vertical migratory regime (relatively speaking, only a small proportion of this species migrate to epipelagic waters, where the Gulf Loop Current flows most swiftly, potentially providing current-mediated transport between the Gulf and the greater Atlantic). To investigate this hypothesis, we integrated biophysical oceanographic modeling data to better define diel vertical migratory regimes and simulate the horizontal migration of these regimes. Our research indicated that access to the swiftest flowing waters of the Gulf Loop Current has real biological impacts on population connectivity between the Gulf and greater Atlantic. Our findings have important implications for the resilience and recovery of populations following natural and anthropogenic disturbances: high connectivity was typically found alongside lower genetic diversity, indicating that a localized die-off following an environmental disturbance may be mediated by the existence of an external genetic reservoir (in the greater Atlantic, for instance). However, high genetic diversity within a species, coupled with population differentiation, may be indicative of local adaptation (though more work is needed to investigate this). If this is the case, these species may be more vulnerable to environmental perturbations as the genetic diversity lost during a localized die-off may not be easily recovered.
DNA barcoding enhances large-scale biodiversity initiatives for deep-sea crustaceans within the Gulf of Mexico and adjacent waters
The application of DNA barcoding represents an alternative and efficient approach to identifying specimens at all stages of their life cycle compared to traditional morphological methods. Currently, DNA barcoding has been applied successfully in a large number of taxonomic groups belonging to both invertebrates and vertebrates, both marine and terrestrial. In addition, DNA barcodes have become an integral part of many descriptions of recently published species. On the other hand, DNA barcoding also allows us to uncover cryptic diversity and may be useful in inferring the evolutionary relatedness between different species. Various traits make mitochondrial markers effective for species identification: relatively easy to amplify, almost exclusively maternal and haploid inheritance with rare recombination, high substitution rates, the absence of introns, with many mitochondrial chromosome copies per cell. The aim of this study is to obtain sequences for the mitochondrial markers (16S and CO1) of marine deep-water pelagic crustaceans from the Gulf of Mexico. Taxonomic and molecular techniques are utilized to document adult crustacean specimens to better understand their taxonomy, life history, evolutionary relationships and cryptic biodiversity. From the 221 species of pelagic crustaceans of the orders Amphipoda, Euphausiacea, Lophogastrida and Decapoda (excluding Portunidae) in the Gulf of Mexico, 104 species have been collected. From the 104 species, we successfully obtained sequences from 81 species. A total of 257 sequences belonging to the 16S gene and 261 sequences belonging to the CO1 gene have been obtained. Evidence of cryptic diversity has been found in the genera Eucopia (Lophogastrida), Allosergestes, Meningodora, and Pasiphaea (Decapoda) and several new distributions records are established. Results are allowing us to question the current classification of several lineages and new evolutionary relationships among species and genera are emerging.