淡水イガイ:ミシガン州の絶滅危惧軟体動物の驚くべき繁殖サイクルを調査する(Freshwater mussels: Investigating the remarkable reproductive cycle of Michigan’s threatened mollusks)

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2024-05-24 ミシガン大学

ミシガン州には43種の淡水二枚貝が生息しており、そのうち30種が絶滅の危機に瀕しています。主な脅威は、外来種の侵入、汚染、そして特にダムの存在です。ミシガン大学の研究者たちは、Huron川とRiver Raisinで淡水二枚貝の研究を行い、その結果をPeerJに発表しました。研究では、二枚貝が魚に寄生するために用いるルアーの多様性を調査し、ルアーが異なる形態を持つことを確認しました。また、この多様性は数十年にわたり安定していることが示されました。特に、ルアーの形態が同じ母貝の産む子貝の中で異なることが発見され、これが単一の遺伝子座によって制御される可能性を示唆しています。この発見は、絶滅危惧種の保護と遺伝子調査のための重要な情報を提供します。

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寄生性淡水イガイLampsilis fasciolaの攻撃的擬態ルアーの多型性 Polymorphism in the aggressive mimicry lure of the parasitic freshwater mussel Lampsilis fasciola

Trevor L. Hewitt, Paul D. Johnson, Michael Buntin, Talia Y. Moore, Diarmaid Ó Foighil
PeerJ  Published:May 24, 2024
DOI:https://doi.org/10.7717/peerj.17359

淡水イガイ:ミシガン州の絶滅危惧軟体動物の驚くべき繁殖サイクルを調査する(Freshwater mussels: Investigating the remarkable reproductive cycle of Michigan’s threatened mollusks)

Abstract

Unionoid freshwater mussels (Bivalvia: Unionidae) are free-living apart from a brief, obligately parasitic, larval stage that infects fish hosts, and gravid female mussels have evolved a spectrum of strategies to infect fish hosts with their larvae. In many North American species, this involves displaying a mantle lure: a pigmented fleshy extension that acts as an aggressive mimic of a host fish prey, thereby eliciting a feeding response that results in host infection. The mantle lure of Lampsilis fasciola is of particular interest because it is apparently polymorphic, with two distinct primary lure phenotypes. One, described as “darter-like”, has “eyespots”, a mottled body coloration, prominent marginal extensions, and a distinct “tail”. The other, described as “worm-like”, lacks those features and has an orange and black coloration. We investigated this phenomenon using genomics, captive rearing, biogeographic, and behavioral analyses. Within-brood lure variation and within-population phylogenomic (ddRAD-seq) analyses of individuals bearing different lures confirmed that this phenomenon is a true polymorphism. The relative abundance of the two morphs appears stable over ecological timeframes: the ratio of the two lure phenotypes in a River Raisin (MI) population in 2017 was consistent with that of museum samples collected at the same site six decades earlier. Within the River Raisin, four main “darter-like” lure motifs visually approximated four co-occurring darter species (Etheostoma blennioides, E. exile, E. microperca, and Percina maculata), and the “worm-like” lure resembled a widespread common leech, Macrobdella decora. Darters and leeches are typical prey of Micropterus dolomieui (smallmouth bass), the primary fish host of L. fasciola. In situ field recordings of the L. fasciola “darter” and “leech” lure display behaviors, and the lure display of co-occurring congener L. cardium, were captured. Despite having putative models in distinct phyla, both L. fasciola lure morphs have largely similar display behaviors that differ significantly from that of sympatric L. cardium individuals. Some minor differences in the behavior between the two L. fasciola morphs were observed, but we found no clear evidence for a behavioral component of the polymorphism given the criteria measured. Discovery of discrete within-brood inheritance of the lure polymorphism implies potential control by a single genetic locus and identifies L. fasciola as a promising study system to identify regulatory genes controlling a key adaptive trait of freshwater mussels.

生物環境工学
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