On the brink of extinction: a new freshwater amphipod Jesogammarusacalceolus (Anisogammaridae) from Japan.

Ko Tomikawa,Naoya Kimura

doi:10.3897/zookeys.1065.71687

Abstract

Freshwater habitats, especially cold springs, are environments in which the risk of extinction faced by organisms remains high due to human activities. To conserve endangered species, it is important to describe and name them. Here, a new, endangered freshwater anisogammarid amphipod species, Jesogammarus (Jesogammarus) acalceolussp. nov., found in a spring in Aomori Prefecture, Japan, is described which is potentially the sole remaining habitat of this species. Both morphological and molecular phylogenetic results strongly support the nesting of the new species within Jesogammarus. Jesogammarus (J.) acalceolussp. nov. is the first species of genus Jesogammarus that was found to lack a calceolus, a sensory organ located on male antenna 2. Thus, the diagnostic criteria for this genus required amendment. A reconstruction of ancestral calceoli, based on a molecular phylogenetic tree, revealed that the common ancestor of Jesogammarus possessed calceoli, which were secondarily lost in J. (J.) acalceolussp. nov. Our results indicate that this new species, which is key to clarifying the evolution of the calceolus, is of high conservation significance.

Highlights

Jesogammarus (J.) acalceolus sp. nov. is the first species of genus Jesogammarus that was found to lack a calceolus, a sensory organ located on male antenna 2
The character state of the most recent common ancestor (MRCA) of J. (J.) acalceolus sp. nov. + J. (J.) hinumensis and J. (J.) acalceolus sp. nov. + J. (J.) hinumensis + J. (J.) ikiensis was the presence of calceolus, with 0.92 and 0.99 proportional likelihood (PL), respectively
The highly diverse genus Jesogammarus, which is found in spring water habitats of the Japanese Archipelago, has a sensory organ termed the calceolus on male antenna 2

Summary

Introduction

It is an important habitat for many aquatic organisms. Freshwater accounts for about 2.5% of all water on Earth [1]. 9.5% of all known species live in fresh water [2]. Deterioration of freshwater environments due to human activities remains a worldwide issue [3, 4]. Species inhabiting freshwater habitats are reported to be at a greater risk of extinction compared to marine and terrestrial species [5,6,7]

Methods

Results

Conclusion