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CURATOR
A pinboard by
Inger Winkelmann

PhD student, Natural History Museum of Denmark

PINBOARD SUMMARY

Figuring out how different giant squids are from each other, and how much they move around globally

Despite being a prominent example of charismatic megafauna, the giant squid, Architeuthis dux, remains a creature shrouded in mystery, with available collections of specimens geographically fragmented and primarily based on dead or moribund specimens, which have washed ashore or ended up as by-catch in commercial trawling nets. A previous molecular study based on 44 such museum specimens from across the world, which used whole mitochondrial genome sequences, found that the level of mitochondrial nucleotide diversity is exceptionally low, adding strong support to the idea that there is only one extant species of giant squid (Architeuthis dux, Steenstrup 1857) and furthermore, a complete lack of phylogenetic structure, indicating complete global panmixia, and that the squid of this species are highly mobile, possibly dispersing over long distances via a drifting paralarval stage. The study presented here follows up on this surprising result, generating a data set of more than 10.000 nuclear genome-wide SNPs derived from a Genotyping-By-Sequencing approach on a subset of 30 samples from those included in the previous study, covering the same major regions of the world’s oceans. Using this new data, the extent of phylogeographic structure in the global population of the giant squid was once more assessed by phylogenetic tree reconstruction and genetic admixture analyses. The new results support the existence of one single global species, but counter to the previous result, the nuclear SNP-based analyses are able to detect signals of phylogeographic structure, dividing the giant squid from the Atlantic, the northern and the southern Pacific Oceans into three distinct population clusters, indicating either the presence of discrete barriers to dispersal and interbreeding between these regions, or a pattern of isolation by distance stretching from the Atlantic, through the Indian Ocean and up to the northern Pacific. The new results showcase an example of mitochondrial and nuclear marker incongruence, and that in the case of some marine organisms a very powerful genetic approach may be necessary in order to pick up on subtle population differentiation. Additionally, they reveal fresh insights into the biology of the elusive giant squid.

5 ITEMS PINNED

Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species.

Abstract: Despite its charismatic appeal to both scientists and the general public, remarkably little is known about the giant squid Architeuthis, one of the largest of the invertebrates. Although specimens of Architeuthis are becoming more readily available owing to the advancement of deep-sea fishing techniques, considerable controversy exists with regard to topics as varied as their taxonomy, biology and even behaviour. In this study, we have characterized the mitochondrial genome (mitogenome) diversity of 43 Architeuthis samples collected from across the range of the species, in order to use genetic information to provide new and otherwise difficult to obtain insights into the life of this animal. The results show no detectable phylogenetic structure at the mitochondrial level and, furthermore, that the level of nucleotide diversity is exceptionally low. These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux (Steenstrup, 1857), and that it is highly vagile, possibly dispersing through both a drifting paralarval stage and migration of larger individuals. Demographic history analyses of the genetic data suggest that there has been a recent population expansion or selective sweep, which may explain the low level of genetic diversity.

Pub.: 22 Mar '13, Pinned: 13 Jun '17

Extraordinary numbers of giant squid, Architeuthis dux , encountered in Japanese coastal waters of the Sea of Japan from January 2014 to March 2015

Abstract: Abstract In total, 57 giant squid, Architeuthis dux, were found between January 2014 and March 2015 in Japanese coastal waters in the Sea of Japan. Occurrences were especially high around Sado Island and in Toyama Bay. All of the squid occurred individually, and 28 were found alive. The occurrences were categorized into three groups based on distance from the shore and the depth at which they were found: (1) washed ashore on a beach or found floating at the surface close to a beach (19 individuals); (2) caught in a fixed net set in coastal waters between 50 and 150 m depths (28 individuals); and (3) caught by bottom trawl or bottom gillnet fisheries several kilometers offshore between 200 and 300 m depths (ten individuals). Two size groups were recognized, one ranging between 80 and 160 cm dorsal mantle length (DML) with a mode at 110 cm and another larger than 160 cm DML. The sex ratio in the smaller group was nearly equal and the larger group was comprised of all females. The Sea of Japan was considered to be a large natural trap for giant squid migrating through southwestern Tsushima Strait.AbstractIn total, 57 giant squid, Architeuthis dux, were found between January 2014 and March 2015 in Japanese coastal waters in the Sea of Japan. Occurrences were especially high around Sado Island and in Toyama Bay. All of the squid occurred individually, and 28 were found alive. The occurrences were categorized into three groups based on distance from the shore and the depth at which they were found: (1) washed ashore on a beach or found floating at the surface close to a beach (19 individuals); (2) caught in a fixed net set in coastal waters between 50 and 150 m depths (28 individuals); and (3) caught by bottom trawl or bottom gillnet fisheries several kilometers offshore between 200 and 300 m depths (ten individuals). Two size groups were recognized, one ranging between 80 and 160 cm dorsal mantle length (DML) with a mode at 110 cm and another larger than 160 cm DML. The sex ratio in the smaller group was nearly equal and the larger group was comprised of all females. The Sea of Japan was considered to be a large natural trap for giant squid migrating through southwestern Tsushima Strait.Architeuthis dux

Pub.: 24 Dec '16, Pinned: 13 Jun '17