Reproductive patterns in syntopic terrestrial isopod species (Crustacea, Isopoda, Oniscidea) from Morocco

Abstract

Summary We compared the reproductive patterns of nine syntopic species of terrestrial isopods from the Oued Laou catchment area, Morocco, with respect to (1) species-specific breeding phenology and (2) reproductive allocation in species of different sizes using laboratory survey data collected over 3 years. All but one species were characterised by seasonal reproduction followed by a sexual rest phase, while ovigerous females of Porcellionides sexfasciatus were present throughout the entire study. Egg production started in April for Philoscia sp., Porcellio dalensis , Porcellio laevis and Porcellionides pruinosus , in May for Armadillidium granulatum and Soteriscus gaditanus , and in June for Agabiformius lentus and Porcellio sp. Thus, under normal environmental conditions, the studied syntopic isopod species exhibited a high degree of overlap in breeding phenology, but species-specific mean female size was negatively correlated with the date of breeding onset; smaller species started breeding later in the year than large species. Several other life-history traits also correlated with species-specific female size. Fecundity was positively correlated with female size in all studied species. The duration of the marsupial period, when the brood pouch contains eggs, embryos or mancae, varied between studied species, lasting 21–24 days in small species ( A. lentus and A. granulatum ) and 49–52 days in large ones ( P. laevis and Philoscia sp.). Reproductive allocation, ranging between 5% ( A. lentus ) and 35% ( P. laevis and P. dalensis ), was positively correlated with female weight. Accordingly, parental investment in producing a juvenile varied between 0.6 mg per manca in the small A. granulatum and 1.6 mg per manca in the large P sexfasciatus . Females of two species reproduced only once in their lifetime. Thus, the smallest of the tested species, A. lentus and A. granulatum are considered semelparous with a low overall reproductive potential of 176 and 320 released juveniles, respectively. By contrast, the iteroparous species P. laevis and P. dalensis exhibited the highest reproductive potential of 2640 and 2432 (juveniles released), respectively; producing, in total, more than six times the offspring of semelparous species. We discuss these findings in the context of species-specific reproductive strategies of co-existing syntopic species.