Life history of the copepod Hemicyclops spinulosus (Poecilostomatoida, Clausidiidae) associated with crab burrows with notes on male polymorphism and precopulatory mate guarding

Abstract

A 25-month field survey was conducted to investigate the life cycle and seasonal population fluctuations in the poecilostomatoid copepod Hemicyclops spinulosus in the burrows of the ocypodid crab Macrophthalmus japonicus in the mud-flats of the Tama-River estuary, central Japan. On the basis of sample collections in the water column and from the crab burrows, it was confirmed that H. spinulosus is planktonic during the naupliar stages and settles on the bottom during the first copepodid stage to inhabit the burrows. Furthermore, the copepods' reproduction took place mainly during early summer to autumn with a successive decrease from autumn to winter. A supplementary observation on the burrows of the polychaete Tylorrhynchus heterochaetus suggested that these burrows are another important habitat of H. spinulosus. There were additional discoveries of male polymorphism and precopulatory mate guarding behavior by males, suggesting an adaptation in the reproductive strategy of this copepod to their narrow habitat spaces and low population densities, in contrast to the congeneric species H. gomsoensis, which co-occurs in the estuary but attains much larger population sizes and is associated with hosts having much larger burrow spaces.

Burrow association of Hemicyclops (Copepoda: Poecilostomatoida) as a possible strategy for predator avoidance

“…Associations with polychaetes have been reported in H. spinulosus (with Tylorrhynchus heterochaetus: Itoh 2001, Itoh & Nishida 2008 and in H. ctenidis (with Neanthes japonica: Ho & Kim 1990). The absence of H. spinulosus in the foregut contents of P. masago, despite the occurrence of the copepods in Macrophthalmus burrows, might be due to the copepods close association with polychaete burrows which would have enabled the copepods to escape from predation by the gobies.…”

“…Food items in the gut contents were identified to major taxonomic categories except for the Hemicyclops species in which the number, species, and developmental stages were also determined whenever possible. The developmental stages of Hemicylops species were identified on the basis of the descriptions by Kim & Ho (1992) and Itoh & Nishida (2007, 2008.…”

“…The major benthic habitats of H. gomsoensis are the burrows of the mud shrimp Upogebia major (de Haan) and those of the ocypodid crab Macrophthalmus japonicus (de Haan). Hemicyclops spinulosus have been found from burrows of M. japonicus and those of the polychaete Tylorrhynchus heterochaetus (Quatrefages) (Itoh 2001, Itoh & Nishida 2007, 2008, while H. ctenidis occurs in the burrows of another polychaete Hediste sp. (referred to as Neanthes japonica (Izuka) in Ho & Kim 1990).…”

Life cycle and precopulatory mate guarding of <i>Goidelia japonica</i> (Copepoda: Poecilostomatoida: Echiurophilidae) associated with the echiuran <i>Urechis unicinctus</i>

“…In Poecilostomatoida, only four species have hitherto been known to have precopulatory guarding behavior, i.e. Pseudomyicola spinosus, Hemicyclops spinulosus Itoh & Nishida, 1998, Pseudanthessius tortuosus Stock, Humes & Gooding, 1964 and Pennatulicola pterophilus (Stock, 1962) (Itoh & Nishida 2008). These species are all symbionts with benthic invertebrates.…”

“…The youngest stages of the four other species guarded by adult males are CIII (Stock et al 1962, Gotto 1979, Do et al 1984, except for H. spinulosus, of which the youngest guarded stage was unknown because observation of precopulatory guarding behavior was made only on a CV female and two adult males collected from the field (Itoh & Nishida 2008). Pseudomyicola spinosus and H. spinulosus start symbiotic life at CI (Do et al 1984, Itoh & Nishida 2008, indicating that adult males do not guard CI or CII, even if they encounter them. Precopulatory mate guarding from mid-or late copepodid stages seems common also in harpacticoid copepods (Kern et al 1984).…”