From five to one: Sandyella species (Palaemonidae) are distinct ontogenetic stages of a single species

Abstract

The palaemonid genus Sandyella includes S. tricornuta (Isla María Madre, Mexico), S. mclaughlinae, S. bicornuta, S. quadricornuta and S. sexicornuta (Clipperton Island, France). These species were first described in the genus Chacella based on collections of few individuals and limited to no ecological information. Sandyella was later erected to differentiate Chacella kerstitchi from Chacella tricornuta and Chacella mclaughlinae. The remaining three Chacella species (<3 mm cephalothorax length) were later also moved to Sandyella and distinguished mainly based on variation in the less than three protuberances on the cephalothorax and number of protuberances on the abdomen. Since their description from their type localities, only Sandyella tricornuta has been additionally recorded from Bahía de La Paz, Mexico. Collections done at 13 locations along the Gulf of California (2009–2010) yielded 2,905 specimens including representatives of all Sandyella species as epibionts of 57 black coral colonies Antipathes galapagensis, which prompted a closer taxonomic examination. Based on observations of live and preserved specimens, including type material, population cephalothorax size frequency and mitochondrial COI data, we inferred that all current Sandyella species (a) exhibit three protuberances on the cephalothorax; (b) cephalothorax length and number of protuberances appear to be progressive among species; (c) species exhibit high COI sequence similarity; and d) the five Sandyella species were observed cohabiting the same black coral colony. Therefore, we conclude that the five current Sandyella species are in fact distinct ontogenetic stages of a single species, S. tricornuta, and our results of a morphological Bayesian analysis led us conclude that this species belongs to the genus Sandyella rather than Chacella.

Continuous Reproduction Causes Stable Population Structure of Antipatharian-Associated Shrimp Sandyella tricornuta (Decapoda: Palaemonidae)

“…It is still unclear whether the small changes in S. tricornuta sex ratio vary seasonally or spatially due to spatial sex segregation, unequal production of males and females, social behavior, or differential mortality rates between sexes. However, adult females of S. tricornuta were on average larger and seem to grow faster than males (Ávila-García et al 2020). The present study demonstrated S. tricornuta has a wide spatial distribution along the islands in the Gulf of California with similar population density and sex proportion favoring encounters of the females with the males consistent with other decapod symbiont species (Correa and Thiel 2003).…”

“…Pronounced protuberances on the cephalothorax and abdomen and a yellow coloration allow S. tricornuta to mimic black coral polyps and go unnoticed (). A recent integrative taxonomic study demonstrated, with population structure, molecular and morphological evidence, that the five species previously described in the genus Sandyella were actually distinct ontogenetic stages of the type species S. tricornuta (Ávila-García et al 2020). This implies that A. galapagensis is the habitat of a single biological species.…”

“…This implies that A. galapagensis is the habitat of a single biological species. All previous studies of Sandyella have focused on taxonomy (Hendrickx 1990, Li 2006, Li and Poupin 2009, Marin 2009, 2010, Ávila-García et al 2020) and distribution range extension (Wicksten and Hernández 2000, Sánchez 2010, Martínez-Guerrero and López-Pérez 2018). However, basic biological and ecological information about reproduction, embryology, larval development, trophic ecology, and population structure of S. tricornuta remain unknown (Ávila-García et al 2020).…”

“…Distribution records of S. tricornuta includes Islas Marías Archipelago (Hendrickx 1990), Clipperton Island (Li 2006, Li and Poupin 2009), Bahía de La Paz (24° N) (Wicksten and Hernández 2000), and the peninsular coast of the Gulf of California (24–30° N) (Sánchez 2010, Ávila-García 2013, 2015, 2020). However, the biogeographic distribution of S. tricornuta is expected to match the distribution of its obligate host A. galapagensis distributed in the Eastern Pacific from the Gulf of California to Peru, at depths from 10 m to 200 m (Sánchez 2010, Lavorato et al 2021) (Table 1).…”

“…SANDYELLA TRICORNUTA (Hendrickx, 1990) is a small (<13 mm total length) obligate ectosymbiont of black coral Antipathes galapagensis Deichmann, 1941 with marked sexual dimorphism and high intraspecific morphological variability throughout its ontogenetic development (Ávila-García et al 2020). Pronounced protuberances on the cephalothorax and abdomen and a yellow coloration allow S. tricornuta to mimic black coral polyps and go unnoticed (Figures S1A,B and S2A,B).…”