Discovery of two new species of eyeless spiders within a single Hispaniola cave

Vision is a remarkable sensory adaptation; however, natural selection may not favor maintenance of eye function in habitats where eyesight does not contribute to fitness. Vision loss is relatively common in cave-dwelling spiders in the temperate zone, but appears rarer in tropical caves. To date, blind spiders in the (sub)tropical Caribbean have only been described from Cuba and Jamaica, including four pholcids, a barychelid, a ctenid, and a prodidomid with reduced eyes. In our survey of over 40 caves in the Greater Antilles, mainly Puerto Rico, Isla Mona, Cuba, and Dominican Republic, we have not previously found any eyeless spiders. Here we summarize information on blind Caribbean spiders, and describe two newly discovered species representing two families, from a single cave, Cueva Seibo, in the Dominican Republic. These are the eyeless Ciba seibo n. gen., n. sp. (Ctenidae) and the vestigial-eyed Trichopebna maddeni n. sp. (Barychelidae). Cueva Seibo appears to be an energy-poor system with a relatively small bat population and is physiologically unique amongst caves we surveyed. We postulate that troglobiomorphism in the Caribbean may result from individual cave environments and hypothesize convergent eye loss within this cave, as most members of both families, including epigean species from the Dominican Republic, have normal eyes. However, another blind species, Ciba calzada (Alayon 1985) n. comb., occurs in a cave in Cuba and it remains to be tested if eye loss occurred in these two convergently, or if their shared lack of eyes is homologous.