Since sponges cannot move, each individual can only fertilize its own egg during sexual reproduction2/21/2024 ![]() Ever since Darwin's epic monographs, these beliefs about possible modes of barnacle mating have been strongly held. ![]() Second, they appear to be constrained by their evolutionary history to exchange sperm either by a form of copulation called pseudo-copulation (release of sperm into a partner's mantle cavity) or, in hermaphrodites, by self-fertilization. First, unlike nearly all free-living arthropods, adults are sessile and typically glued to hard surfaces. Textbooks note two bizarre observations about typical stalked and acorn barnacles (Thoracica). These observations (i) overturn over a century of beliefs about what barnacles can (or cannot) do in terms of sperm transfer, (ii) raise doubts about prior claims of self-fertilization in barnacles, (iii) raise interesting questions about the capacity for sperm capture in other species (particularly those with short penises), and (iv) show, we believe for the first time, that spermcast mating can occur in an aquatic arthropod. Sperm capture may therefore be a common supplement to pseudo-copulation in this species. Replicate subsamples of individual egg masses confirmed that eggs fertilized by captured sperm occurred throughout the egg mass. Sperm capture occurred in 100 per cent of isolated individuals and, remarkably, even in 24 per cent of individuals that had an adjacent partner. ![]() Using 16 single nucleotide polymorphism markers, we confirmed that a high percentage of eggs were fertilized with sperm captured from the water. ![]() To test these alternative hypotheses, we collected isolated individuals bearing egg masses, as well as isolated pairs where at least one parent carried egg masses. They must therefore either self-fertilize or-contrary to all prior expectations about barnacle mating-obtain sperm from the water. Although the common northeast Pacific intertidal gooseneck barnacle, Pollicipes polymerus, is believed only to cross-fertilize, some isolated individuals well outside penis range nonetheless bear fertilized eggs. Most free-living barnacles are hermaphroditic, and eggs are presumed to be fertilized either by pseudo-copulation or self-fertilization. ![]()
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