Krug - Frustrated virgins and reproductive flexibility in the sacoglossan sea slug Alderia: how hypodermic insemination affects selfing and speciation

Frustrated virgins and reproductive flexibility in the sacoglossan sea slug Alderia: how hypodermic insemination affects selfing and speciation

Patrick J. Krug

California State University, Los Angeles, CA 90032-8201, pkrug@calstatela.edu

Sacoglossan sea slugs live and feed on species-specific host algae, and their planktonic larvae metamorphose in response to host-produced cues. Coevolution between slugs in the genus Alderia and their host algae Vaucheria spp. has produced complex dispersal strategies and cryptic speciation in Californian populations. I will discuss how hypodermic insemination leads to self-fertilization and inappropriate sex between species. The southern Alderia sp. displays a rare reproductive polymorphism, producing long-lived planktotrophic larvae or short-lived lecithotrophic larvae. Virgin slugs, metamorphosed and reared in isolation, produced unfertilized egg masses 5 days after reaching reproductive maturity; unfertilized clutches were significantly larger than fertilized clutches of paired control slugs, suggesting mating costs normally reduce fecundity. Virgin slugs began self-fertilizing 5 days after initial egg production, a phenomenon only reported for 2 other opisthobranchs, both sacoglossans. Planktotrophic virgins lowered their fecundity to control levels after selfing, whereas lecithotrophic virgins produced more eggs per clutch whether unfertilized or self-fertilized, compared to mated controls. Development mode and sexual history therefore interactively affect energy allocated to reproduction. Selfing via accidental auto-injection may be a common consequence of hypodermic insemination that has gone unnoticed due to sperm storage abilities of sacoglossans. The sibling species of Alderia overlap without hybridizing, and cross-inseminations in the lab normally yield no offspring, suggesting post-zygotic isolation has arisen. Hypodermic insemination precludes most forms of pre-zygotic isolation seen in other organisms; I therefore propose that in sacoglossans, sister species will occupy different algae in sympatry, achieving reproductive isolation pleiotropically as a by-product of host choice behavior.