Evaluating Reproductive Strategies and Female Bateman Gradients in Ditrema temminckii: Is the Number of Fathers a Good Approximation for the Number of Mates?
Surfperches (Embiotocidae) are a unique family of viviparous fishes that have internal fertilization, gestation to the sub-adult stage, and live-birth; therefore, maternal investment is extremely high. This invokes the expectation that brood size is limited and females should be choosy and select few mates. Yet multiple paternity occurs in all eight species examined to date, with high prevalence ranging from 92–100%. Most surfperches are found along the Eastern Pacific coast, but Ditrema temminckii is distributed in the Western Pacific and we found differences in their mating strategy compared to other surfperches. In D. temminckii, prevalence of multiple paternity was only 60%. Further, the average number of sires was only 1.86 per brood even though brood sizes ranged from 12–45, and paternity was skewed, with the majority of paternity allocated to a single male. We propose that these differences may be associated with strong female selection on males in this species. Finally, we evaluated whether the number of fathers is an accurate estimate for the number of mates by comparing the number of alleles detected from fathers within the brood to the number of alleles from mates via genotyping alleles from spermatozoa within the uterine sac and found no significant difference, suggesting that the number of sires is a reasonable estimate for the number of mates in D. temminckii.

Reproductive cycle of Ditrema temminckii characterized by gonadosomatic index (GSI) of males and females off Sado Island, Niigata. Males are represented by blue diamonds (n = 42) and females by red circles (n = 127). Black outline indicates pregnant females (n = 19). Immature females <145 mm SL are represented by pink triangles (n = 72).

Relative paternal contribution to the brood of D. temminckii. Paternity was assigned to broods of D. temminckii. Each bar represents all the offspring of a single female, and the colors represent the contribution of each genetically distinct sire.

Comparison of the number of alleles from mates vs. sires for two loci (Dte2 and Dte5) in D. temminckii; each circle represents the number of observations. (A) Alleles contributed by mates (uterine sacs blue, = 5.66, n = 6) and sires (brood red, = 6.6, n = 15). We did not detect a statistical difference between the two (paired t-test, t = 1.39, P = 0.18). (B) One-year-old females SL 145–165 mm. Alleles contributed by mates (uterine sacs, blue, = 5.66, n = 6) and sires (brood, red, = 6.28, n = 7). We did not detect a statistical difference between the two (paired t-test, t = 1.35, P = 0.22).
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