Pair-living is a common social system found across animal taxa, and the relationship between pair-living and reproduction varies greatly among species. Siphonaria gigas, hermaphroditic pulmonate gastropods, often live in pairs in the rocky intertidal zone of the tropical Eastern Pacific. Combining genetic parentage analysis using four polymorphic microsatellite loci with behavioral observations from a 10-week field study, we provide the first description of the mating system of a Siphonaria species incorporating genetic data. S. gigas mated both within-pair and extra-pair and three out of four paired S. gigas individuals produced egg masses with extra-pair paternity. Multiple paternity was detected, but at a relatively low frequency (19% of egg masses) compared to other marine gastropods. Behavioral data indicate one potential advantage of pair-living: paired S. gigas produced almost twice as many egg masses as their solitary counterparts over four reproductive cycles. These observations, together with constraints on the movement of S. gigas, suggest that pairing may ensure mate access and increase reproductive success.

This dataset includes genomic libraries for four Siphonaria gigas individuals. Foot tissue was collected from live adult S. gigas and stored in 99% ethanol. DNA was extracted from the tissue using the Qiagen DNeasy Blood and Tissue Kit with a modified elution step (see manuscript for details). Shotgun genomic libraries were prepared using a simplified restriction-associated digestion sequencing protocol (after Toonen et al. 2013), including digestion with DpnII. The digested DNA was purified and then prepared for sequencing using a KAPA Hyper Prep Kit (Kapa Biosystems Ltd.) and Illumina TruSeq adapters (Illumina Inc.). Libraries were sequenced on an Illumina MiSeq platform with V3 chemistry and 600 cycles to produce 300 bp paired-end reads. The raw sequence data from the four S. gigas are provided here; full methods are provided in the open-access publication.

Further details of sequencing and processing included in manuscript.