One shark, one global population?
We recently highlighted the lack of population genetic studies within marine environments, and noted that the existing ones show exciting results about both barriers and corridors for dispersal. A new paper (open) investigated the global population structure of the blue shark (Prionace glauca). This species has a serious global oceanic distribution through both temperate and tropical waters of the Atlantic, Pacific, and Indian oceans! Blue sharks are also a species of conservation concern as they are near threatened because they get caught as by-catch during commercial fishing; IUCN estimates 20 MILLION individuals are taken annually! (See our piece here on how to reduce your contribution to bycatch.) The authors found that blue sharks have a single global population. This result was unexpected given the large range and potential for local adaptation, although better genome sampling may produce different results. On some levels this makes the conservation of sharks easier, as any restocking would not require genetic background to be accounted for; but it can also make things harder as it may be difficult to monitor local population size changes.
Fossils don’t Speciate because They’re Dead; but Living Fossils Can
“Living fossils” are currently living species that closely resemble extinct species known only through the fossil record. Living fossils are of particular interest because they often represent the last (or last few) species within an entire lineage of life’s diversity. This paper (sub) sampled Nautilus and Allonautilus in Oceania then investigated both the number of species and population structure within each species. The authors inferred multiple species within their dataset, despite samples having similar morphologies and suggest that cryptic speciation may be a feature within living fossils. This paper has clear conservation implications as they first delineate species, but also observed that population sizes were lower for isolated islands than continental shelf populations which may have increased gene flow. Thus, the authors suggest how to prioritize ecosystem conservation to maintain nautilus populations.
Generalists Declining with Climate Change
Species distribution models are a powerful way to understand the landscape and climatic factors which limit a species’ range. Scientists are able to take those models one step further by forecasting the model into IPCC estimates of future climatic conditions. This paper (sub) investigates these forecast models for the reef building lobe coral (Porites lobata); specifically, the authors ask how the distribution of this coral will expand or contract under varying climate change scenarios by 2100. The expectation is that as a generalist species tolerant of high climatic variability that the species will expand its range. However, when the authors ran the species distribution models based on population structure, suitable areas for the coral decreased by ~50% globally, including some geographic regions where extinction was predicted. While global versus structured population species distribution models often give different results, this one is surprising due to how much habitat loss was predicted. Lobe corals are listed as near threatened by the IUCN due to climate change (as discussed in this paper) but also increased disease prevalence with warmer temperatures and some poaching for aquariums. Given the predictions of local extinction, out-of-the-box conservation measures such as genome editing to increase physiological tolerance may be needed, but it is worth noting that this is a particularly slow growing species, thus the best conservation measures will be to slow the impacts of climate change.
Side photo of Nautilus pompilius by Reinhard Dirscherl via ARKive.