Deep-water Lineage Research Articles

Temperature adaptation in larval development of lithodine crabs from deep-water lineages

Adaptations in per-offspring investment and larval development are considered to have been crucial to the global radiation of deep-water lineages of lithodine crabs (Lithodinae). Temperature is proposed to drive latitudinal trends in energy provisioning of eggs in marine invertebrates, mediated by thermally dependent intraspecific plasticity in per-offspring investment. Consequently, a changing climate may be expected to directly affect larval provisioning. We analysed available data to examine any differences in per-offspring investment and larval development among deep-water lineage lithodines. Although data are few, interspecific differences in the thermal scope of deep-water-lineage lithodine larvae appear coupled with differences in biogeography. This coupling suggests environmental temperature influences larval thermal scope. Lithodine phylogeography suggests that larval cold-eurythermy in deep-water-lineage lithodines is a derived trait that has evolved in relatively warm and variable subantarctic shallow water. Therefore, we hypothesise that capacity to adapt to warmer and more variable environmental conditions may afford deep-water-lineage lithodines some resilience to ocean warming, depending on the rates of environmental and adaptive change. Interspecific comparisons also suggest that larval duration and per-offspring investment are positively correlated. Faster development at a given temperature is associated with higher respiration rates and greater energetic reserve utilisation. Therefore, we hypothesise that selection pressure for contrasting metabolic adaptations in different thermal environments contributes to shifts in larval duration and per-offspring investment.

Temperature effects on larval development in the lithodid crab Lithodes maja

Physiological adaptations enabling tolerance of low temperature, as well as adaptations in larval development, are thought to be critical to the global radiation of deep-water lineages of lithodine crabs. However, global climate change is warming the oceans, potentially impacting the biogeographic distributions of these large predatory crabs. To date, larval thermal scope has only been explored in a few deep-water lineage lithodines. We assessed larval development parameters in the northern stone crab Lithodes maja at temperatures ranging from 1 °C to 15 °C. We examined larval survival, duration of development, energetic reserve utilisation, and respiration rate. L. maja larvae displayed a narrow thermal tolerance window and metamorphosed successfully at 6 °C only. Differential uses of energetic reserves among temperatures during development in L. maja support the interpretation of a narrow larval thermal scope and indicate that 6 °C is the optimum temperature for development in this species. Consequently, continued ocean warming is likely to force biogeographic range shifts in L. maja.

Evolutionary History of Lake Tanganyika's Predatory Deepwater Cichlids.

Hybridization among littoral cichlid species in Lake Tanganyika was inferred in several molecular phylogenetic studies. The phenomenon is generally attributed to the lake level-induced shoreline and habitat changes. These allow for allopatric divergence of geographically fragmented populations alternating with locally restricted secondary contact and introgression between incompletely isolated taxa. In contrast, the deepwater habitat is characterized by weak geographic structure and a high potential for gene flow, which may explain the lower species richness of deepwater than littoral lineages. For the same reason, divergent deepwater lineages should have evolved strong intrinsic reproductive isolation already in the incipient stages of diversification, and, consequently, hybridization among established lineages should have been less frequent than in littoral lineages. We test this hypothesis in the endemic Lake Tanganyika deepwater cichlid tribe Bathybatini by comparing phylogenetic trees of Hemibates and Bathybates species obtained with nuclear multilocus AFLP data with a phylogeny based on mitochondrial sequences. Consistent with our hypothesis, largely congruent tree topologies and negative tests for introgression provided no evidence for introgressive hybridization between the deepwater taxa. Together, the nuclear and mitochondrial data established a well-supported phylogeny and suggested ecological segregation during speciation.

DEEP UNDER THE SEA: UNRAVELING THE EVOLUTIONARY HISTORY OF THE DEEP-SEA SQUAT LOBSTER PARAMUNIDA (DECAPODA, MUNIDIDAE)

The diversification of Indo-Pacific marine fauna has long captivated the attention of evolutionary biologists. Previous studies have mainly focused on coral reef or shallow water-associated taxa. Here, we present the first attempt to reconstruct the evolutionary history--phylogeny, diversification, and biogeography--of a deep-water lineage. We sequenced the molecular markers 16S, COI, ND1, 18S, and 28S for nearly 80% of the nominal species of the squat lobster genus Paramunida. Analyses of the molecular phylogeny revealed an accelerated diversification in the late Oligocene-Miocene followed by a slowdown in the rate of lineage accumulation over time. A parametric biogeographical reconstruction showed the importance of the southwest Pacific area, specifically the island arc of Fiji, Tonga, Vanuatu, Wallis, and Futuna, for diversification of squat lobsters, probably associated with the global warming, high tectonic activity, and changes in oceanic currents that took place in this region during the Oligocene-Miocene period. These results add strong evidence to the hypothesis that the Neogene was a period of major diversification for marine organisms in both shallow and deep waters.