Zenopontonia soror caridean shrimp exhibits dynamical mimicry with sea star host switching

Abstract

Zenopontonia soror (Nobili, 1904) (Caridea: Palaemonidae) is a shrimp symbiont of several sea star species that exhibits homochromy with distinct mimetic coloration according to host species. To date, populations of Z. soror have been studied extensively in the Indo-Pacific and Gulf of Panama; however, those present in the Gulf of California (Mexico) have not been evaluated. Here we conduct the first evaluation of the diversity of chromotypes present in Z. soror populations in Bahía de La Paz (Baja California Sur, Mexico), and experimentally tested how long shrimp take to archieve mimicry post sea star switch. We hypothesized that Z. soror individuals rapidly change coloration (minutes to few hours) throughout their ontogeny to mimic the coloration of host species to decrease risk of predation. This hypothesis was tested by translocating Z. soror individuals to a different sea star species with different coloration and background in the field and under laboratory conditions for three consecutive days. At least 18 chromotypes of Z. soror were identified among 386 observed specimens based on the RGB color system; and colors were independent of body size. Each chromotype holds different relative abundance in the population. Coloration was not distinctive of each individual, while color intensity increased along ontogeny development from semi-transparent (juveniles) to solid coloration (adult phase). Dynamic contraction or dispersion of the chromatophores (pigment migration) caused changes in coloration to resemble coloration of the basibiont sea star. Full mimicry of new host was achieved within 36 h in field and laboratory conditions. Zenopontonia soror individuals were observed to mimic the white spines of the sea star host Acanthaster solaris by exhibiting a white dorsal band, while others selected color-concealing hosts to stay cryptic for a short time. We conclude that Z. soror dynamically shifts coloration as an adaptation to match the symbiont shrimp–sea star host coloration to minimize or prevent predation, but individuals are vulnerable to be detected by visual predators during the color transition (<36 h period). The combined use of the Hogben and Slome index and the RGB color system from digital images provide the most precise method to assign intensity and color in epibiont-host organisms to understand the complex process of homochromy.