The symbiotic shrimpAscidonia flavomaculatalives solitarily in the tunicateAscidia mentula: implications for its mating system

Abstract

Symbiotic crustaceans are expected to live solitarily with their hosts when members of their host species are small (relative to symbiont body size) and structurally simple. We tested the hypothesis of a solitary lifestyle in Ascidonia flavomaculata, a symbiotic shrimp that inhabits the branchial chamber of the relatively small and structurally simple tunicate Ascidia mentula in the subtidal zone of the Islas Baleares, Spain. We found that members of A. flavomaculata dwell as solitary individuals in the branchial chamber of ascidians at a higher frequency than expected by chance alone. Given this host use pattern of A. flavomaculata, we hypothesized that males actively move among host individuals in search of receptive females. We provide several lines of evidence consistent with that hypothesis. First, a positive correlation between shrimp and host body size was detected for females, but not for males, during one of the sampling seasons. If males as well as females spend long periods of time within their host individuals, a positive correlation between shrimp and host body size should have been found for both males and females. Second, the body sizes of individuals in the few male-female pairs observed during this study were poorly correlated. If males of A. flavomaculata shared their host individuals with females for long periods of time, a positive correlation between the sizes of males and females in a pair should have been found. Lastly, the body sizes of paired males were larger than those of solitary males during summer, when reproduction was more intense. This difference in body size between paired and solitary males additionally suggests competition among putatively roaming males for receptive females. Manipulative experiments and behavioral observations are necessary to reveal the details of the mating system of A. flavomaculata and other symbiotic crustaceans with a solitary lifestyle.

Host-use pattern of the shrimp Periclimenes paivai on the scyphozoan jellyfish Lychnorhiza lucerna: probing for territoriality and inferring its mating system

“…Also, in P. paivai, sex specific differences in mortality rates by predators, driven by a greater propensity of males (compared to females) to switch among host individuals (see above), could lead to the observed sex ratio being skewed towards females in the population. Female-skewed sex ratios have been reported before in other symbiotic and free-living crustaceans in which males frequently roam among hosts in search of receptive females [12,61]. By contrast to that reported for P. paivai, the sex ratio is hardly ever skewed in favor of females in populations of symbiotic crustaceans that do not or rarely switch among host individuals, and that exhibit a monogamous mating system [15,26,31].…”

“…Also in agreement with theory, other symbiotic species live in large non-territorial aggregations in naturally abundant, relatively large and morphologically complex host species [18,27]. Although our understanding about the environmental conditions driving the host-use pattern of symbiotic crustaceans has improved considerably during the last decade (e.g., [12,25]), more studies are needed before major generalizations regarding the mechanisms explaining the social behavior of symbiotic crustacean can be formulated.…”

“…The host-use pattern and population distribution of symbiotic crustaceans also vary widely. For instance, some symbiotic crustaceans inhabit their hosts as solitary individuals: Inachus phalangium (Fabricius, 1775) [10], Petrolisthes spinifrons (H. Milne Edwards, 1837) [11], Ascidonia flavomaculata (Heller, 1864) [12]; in heterosexual pairs: Pinnixa transversalis (H. Milne Edwards & Lucas, 1842) [13], Alpheus armatus Rathbun, 1901 [14], Pontonia margarita Verrill, 1869 [15]; or in aggregations: Periclimenes anthophilus Holthuis & Eibl-Eibesfeldt, 1964 [16], Petrolisthes mitra (Dana, 1852) [17], Thor amboinensis (De Man, 1888) [18]. Even other symbiotic crustaceans form complex societies i.e., the sponge-dwelling eusocial shrimp Synalpheus regalis Duffy, 1996 [19].…”

The ascidian-associated shrimp Ascidonia miserabilis (Caridea: Palaemonidae): first record for Brazil and additional records for the Caribbean Sea

“…The genus Ascidonia Fransen, 2002 includes small-sized (total length usually less than 15 mm) commensal shrimps living in branchial basket of tunicates, mostly of the genus Ascidia Linnaeus, 1767 (Fransen, 2002(Fransen, , 2006Baeza & Díaz-Valdés, 2011). The five presently known species of Ascidonia are distributed in the eastern Pacific (A. californiensis (Rathbun, 1902), A. pusilla (Holthuis, 1951)), the western Atlantic (A. miserabilis (Holthuis, 1951)), the eastern Atlantic (A. flavomaculata (Heller, 1864)), and both the eastern and western Atlantic (A. quasipusilla (Chace, 1972)).…”

Modiolarca lateralis (Pteryomorphia: Mytilidae): bivalve associated to six species of ascidians from Bocas del Toro, Panama

“…Many invertebrates may find refuge within ascidians, including commensal amphipods (Thiel, 2000), shrimps (Baeza & Díaz-Valdés, 2011) and parasitic copepods (Boxshall, 2005). Cyanobacteria may also be found in the tunic (López-Legentil et al, 2011), along with micro-filamentous algae (Lambert et al, 1996) and invertebrates.…”