Phylogeny and evolution of Loxoconcha (Ostracoda, Crustacea) species around Japan

Abstract

The pore-systems of 17 extant species of Loxoconcha around Japan were studied in order to understand their phylogeny and evolution. The phylogeny was estimated by two steps. First, the 17 species were divided into two groups, Group A (12 species) and Group B (five species) by Pore pattern Below Eye tubercle (PBE) analysis. Then, intragroup relationships were estimated by Differentiation of Distributional pattern of Pore-system (DDP) analysis. PBE analysis reveals that species of Groups A and B have on average different ecological preferences. Species of Group A, which appeared in the late Pliocene, are more diverse, have both phytal and bottom-dwelling modes of life, possess fewer pore-systems in the ventral area, and inhabit normal marine environments. Species of Group B, whose oldest fossil record is the lower Miocene, are less diverse, have only bottom-dwelling species, possess more pore-systems in the ventral area, and tend to inhabit brackish water environments. The results of this study suggest that the differences in ecology may have had an impact on the late Cenozoic diversification around Japan. The primary invasion of Group B occurred before the lower Miocene,with no subsequent diversification. Group A invaded after the late Pliocene and immediately diversified, which created the present abundance of Loxoconcha species around Japan in both species diversity and variety of modes of life.

Three new species of the genus Loxoconcha (Crustacea, Ostracoda, Podocopida) from the Okinawa Islands, southern Japan

“…nov. and L. santosi sp. nov., share the same distributional pattern of pore systems located below the eye tubercle, belonging to Group B, according to Ishii et al (2005) (Fig. 14A, B).…”

“…Palmoconcha, Sagmatocythere and Loxocorniculum, the effective species number of Loxoconcha must be smaller. More than twenty living and four fossil species have been described so far from Japan (Ishii et al 2005;Ozawa & Ishii 2008).…”

“…The migration and speciation patterns of four species of the L. japonica species group were presented. Fourthly, Ishii et al (2005) studied 17 species of Loxoconcha around Japan, and concluded that they were divided into two groups according to the distribution pattern of the pore systems located below the eye tubercle. The Group A is more diverse, but has fewer pore systems in the ventral area than Group B, and tends to inhabit normal marine environments, while the Group B inhabits brackish water.…”

The History of Sexual Dimorphism in Ostracoda (Arthropoda, Crustacea) Since the Palaeozoic

“…However, except for the The History of Sexual Dimorphism in Ostracoda (Arthropoda, Crustacea) Since the Palaeozoic 65 horn-like protuberance, the carapace appearance of species of this genus, including Loxocorniculum mutsuense from Japan, is very similar to that of the genus Loxoconcha as noted by Ishii et al [63]. The phylogenetic independence of Loxocorniculum in Japan as a genus distinct from Loxoconcha has been debated [16].…”

“…The phylogenetic independence of Loxocorniculum in Japan as a genus distinct from Loxoconcha has been debated [16]. Therefore this chapter tentatively includes Loxocorniculum mutsuense, first proposed as a new species from Japan by [66], in the genus Loxoconcha following the opinion of Ishii et al [63].…”