Having cake and eating too: The benefits of an intermediate larval form in a brittle star Amphiodia sp. opaque (Ophiuroidea)

Abstract

Most marine invertebrate larvae either obligately feed or depend on maternally provided reserves during planktonic development. A small number of species have the capacity to do both, in a mode of development known as facultative planktotrophy.We describe facultative feeding in a larva from the Oregon coast, and identify it as being an undescribed species in the genus Amphiodia, which we refer to as Amphiodia sp. opaque. We quantified the effects of food on larval and juvenile quality by culturing larvae, collected as embryos, with and without microalgal food at 15°C. The resulting juveniles were monitored under conditions of starvation. A cohort of juveniles of larvae caught as plankton was subjected to the same starvation treatment for comparison with our laboratory-reared larvae. We observed benefits to offspring that received food: larvae provided with microalgae developed more quickly and metamorphosed at higher rates. Furthermore, juveniles resulting from fed larvae were larger and were able to avoid starvation for longer after metamorphosis. Our results varied across two experimental years, suggesting that provisions provided by parents vary between populations and years. Juveniles from planktonic larvae exhibited sizes not statistically different from larvae cultured in the absence of food, but died from starvation more quickly.

Evo‐devo in the ophiuroid family Ophiocomidae

“…Macrophiothrix rhabdota, are 140 and 230 μm in diameter, respectively (Nakata & Emlet, 2023;Podolsky & McAlister, 2005). Eggs of these sizes were not present in the Ophiocomidae.…”

“…There was a gap in egg size distribution in the ophiocomids between 100 and 300 μm diameter, the intermediate egg size observed in ophiuroids with facultative planktotrophic larvae (the ability to develop to metamorphosis in the absence of an exogenous food source) (Allen & Pernet, 2007;Nakata & Emlet, 2023). The eggs of the two ophiuroid species known to have these larvae, Amphiodia sp.…”

“…The gap in the egg size distribution indicates the absence of facultative planktotrophy in ophiocomids. Facultative planktotrophy and intermediate larval forms are rare in marine invertebrates (Collin, 2012) and in echinoderms are only known for four species (Allen & Podolsky, 2007;Emlet, 1986;Hart, 1996;Nakata & Emlet, 2023). It is suggested that facultative planktotrophy is an evolutionarily unstable strategy because of rapid evolution of lecithotrophy through a facultative planktotrophic larva that was quicky lost (Allen & Pernet, 2007;Wray, 1996).…”

“…The yolky larvae of Amphiodia sp. have short arms, and the posterodorsals are reduced or absent so that most larvae only have six arms (Nakata & Emlet, 2023). Plasticity in development of the eighth pair of ophiopluteal arms is common in ophiuroids (Fell, 1945;Mortensen, 1931;Nakata & Emlet, 2023).…”

“…Although there are studies of developmental evolution for four ophiuroid genera-Amphiodia, Ophionereis, Ophiothrix, and Macrophiothrixonly the latter included a detailed molecular phylogeny (Hart & Podolsky, 2005;Nakata & Emlet, 2023;, 2006.…”