No effect of group size on sex allocation in a protandric-simultaneous hermaphroditic shrimp

Abstract

Lysmata wurdemanni is a protandric-simultaneous hermaphroditic shrimp. Individuals reproduce as males first and late in life as simultaneous hermaphrodites. I examined whether sex allocation (resources devoted to ova vs sperm) varies with group size in shrimps that have just matured as hermaphrodites. Focal males were reared with different numbers of hermaphrodites (1, 2, 5 or 10). Sperm stored in the ejaculatory ducts and eggs brooded underneath the abdomen were retrieved and weighted immediately after focal shrimps matured as hermaphrodites. Hermaphrodites should invest more into sperm with increasing group size to cope with more intense sperm competition. The proportion of focal shrimps that lost their first clutch of eggs after maturing as hermaphrodites increased with group size. This suggests male gender preferences by hermaphrodites experiencing large group sizes. No differences in sex allocation among group sizes were recorded for shrimps that did not lose their first clutch of eggs. Thus, group size does not affect sex allocation in terms of ova and sperm mass. This lack of phenotypic plasticity might be explained if sperm competition is not important in L. wurdemanni. It should not pay in terms of fitness for shrimps to produce and inseminate female-role hermaphrodites with large amounts of sperm when full paternity is assured in the absence of multimale mating. In agreement with this idea, a second experiment demonstrated that female-role hermaphrodites invariably mated only once with a single other shrimp.

Molecular phylogeny of shrimps from the genus Lysmata (Caridea: Hippolytidae): the evolutionary origins of protandric simultaneous hermaphroditism and social monogamy

“…These functional simultaneous hermaphrodites have been termed female‐phase individuals or simultaneous hermaphrodite phase individuals by Bauer (2000) and Baeza (2006), respectively. Because most studies employ the term ‘simultaneous hermaphrodite’ or some variation thereof (Lin & Zhang, 2001; Baeza, 2006, 2007a, b, c; Calado & Dinis, 2007), the terms males and hermaphrodites are used hereafter to describe the two sexual phases.…”

Molecular systematics of peppermint and cleaner shrimps: phylogeny and taxonomy of the genera Lysmata and Exhippolysmata (Crustacea: Caridea: Hippolytidae)

“…The adaptive value of this unusual sex allocation pattern is currently being studied in various species (Bauer, 2000, 2006; Lorenzi et al. , 2005; Baeza, 2006, 2007a, b, c).…”

“…the red blood shrimps Lysmata splendida and Lysmata debelius , and the skunk and/or lady scarlet shrimps Lysmata amboinensis and Lysmata grabhami ; Limbaugh, Pederson & Chace, 1961; Bruce, 1983; Fiedler, 1998; Baeza, 2009). Because of this lifestyle diversity, shrimps from the genus Lysmata and Exhippolysmata have captured the attention of behavioural ecologists, and are currently being used to explore the importance of the environment in favouring particular behavioural and morphological innovations (Baeza & Bauer, 2004; Baeza, 2006, 2007a, b, c, 2008, 2009).…”

Sex Allocation Adjustment to Mating Group Size in a Simultaneous Hermaphrodite

“…For instance, field studies have shown that male allocation is positively related to population density, which suggests that individuals invest more resources into the male sex function if competition for mating partners is high under natural conditions (e.g., Raimondi and Martin 1991;Hart et al 2010). Similarly, experimental studies on a broad range of simultaneously hermaphroditic animal species provide evidence that individuals invest relatively more resources into the male sex function when kept in larger groups under laboratory conditions (e.g., Trouvé et al 1999;Schärer and Ladurner 2003; but see Koene et al 2006;Baeza 2007). However, in all of these studies it was unknown how density and/or social group size (i.e., the number of potential mating partners within a group) actually translated into the corresponding mating group size.…”