About me: I was a lab apprentice at Roswell Park Cancer Institute in Buffalo, New York in 2008. Making gels and using trypsin digestion protocols was my game. I volunteered at the Seattle Aquarium as an interpreter and a lab technician. I graduated with a Bachelor of Science in Aquatic Fishery and Science at the University of Washington in 2010. Then I was a field intern for Wild Fish Conservancy surveying juvenile salmon and other fish species for habitat restoration projects in Grays Harbor County in 2011.
Multiple paternity in the Big Skate: Exploring Post-Copulatory-Sexual-Selection in the Development of the Offspring
I am interested in looking at multiple paternity of Big skates (Beringraja binoculata , Girard 1855). Currently there’s only two species that are known to have more than one embryo in an egg case, the Mottled skate (Beringraja pulchra ) is the other species. I want to know if the females are selectively choosing the males may result in how the embryos are sired, and seeing if the individual development rates differ in the egg cases themselves.
Thesis Project summary:
Polyandry is defined as the action of a female mating with more than one male. Polyandry results in multiple paternity (MP), where a single brood is sired by multiple males (Daly-Engel et al. 2010).This mating strategy may contribute to maintaining a genetically diverse population, but the benefits of such a strategy are still being explored in elasmobranchs which don’t exhibit additional parental care (DiBattista et al. 2008; Coleman and Jones 2011). While fecundity is higher in oviparous species than viviparous species, evidence of MP in oviparous species has yet to be explored in-depth (Daly-Engel et al. 2010; Fitzpatrick et al. 2012). Currently, there are two oviparous species in the Eastern Atlantic Ocean that are known to exhibit MP: the Small-spotted catshark (Scyliorhinus canicula) (Griffiths et al. 2011) and the Thornback ray (Raja clavata) (Chevolot et al. 2007). As of now, no studies have explored whether skates endemic in the Eastern Pacific Ocean exhibit MP or whether post-copulatory-sexual-selection contributes to the development of the offspring.
Skates have dorso-ventrally flattened morphology; many are benthic dwellers associated with soft bottoms, thus vulnerable to bottom trawling. Fisheries management policies must account for the different reproductive life histories of species. All skates are oviparous (egg-laying), however, some skate species exhibit late sexual maturity and slow growth like other elasmobranchs, complicating while others mature more quickly and have the capability of reproducing actively year round (Ebert et al. 2008; Winton et al. 2013; James et al. 2014). One species that exhibits the unique strategy of reproducing actively year around is the Big skate (Beringraja binoculata) (J. Bizzarro, University of Washington and D. Ebert, Moss Landing Marine Labs, unpubl. data).
Out of the 289 species of skates known, only two possess the unique trait of producing multiple embryos (1-8) within an egg capsule. The Big skate and the Mottled skate (Beringraja pulchra) are currently the only two species that exhibit this novel reproductive characteristic. However, Big skates are arguably the most fecund of any known elasmobranch. This is supported by an earlier sexual maturity (5-8 years) than most species of skates, being reproductively active year round, and having the unique characteristic of producing multiple embryos (range: 1-8) within a single egg case (Hitz 1964). In a lifetime, a single female may produce more than 48,000 embryos (Ebert and Davis 2007; Ebert et al. 2008). These observations have prompted additional questions concerning whether multiple paternity is present due to the unique mode of oviparity of this species, as well as if the offspring development time is influenced by the sires’ genetic traits.
My study will focus on the following objectives:
• Examine whether multiple paternity is present in Big skates
• Determine if the offspring development time varies with different fathers within in an egg case
• Assess whether the frequency of multiple paternity, the number of embryos, the size of the embryos, the and sex ratio of the offspring varies geographically in the Eastern North Pacific
Barnett LK, Winton MV, Ainsley SM, Cailliet GM, Ebert DA. 2013. Comparative demography of skates: Life-History correlates of productivity and implications for management. PloS one 8(5):e65000. Doi:10.1371/journal.pone.0065000
Chevolot M, Ellis JR, Rijnsdorp AD, Stam WT, Olsen JL. 2007. Multiple paternity analysis in the thornback ray Raja clavata L. Journal of Heredity 98:712–5.
Chiquillo KL, Ebert DA, Slager CJ, Crow KD. 2014. The secret of the mermaid’s purse: Phylogenetic affinities within the Rajidae and the evolution of a novel reproductive strategy in skates. Molecular Phylogenetics and Evolution (75): 245–251. DOI: 10.1016/j.ympev.2014.01.012
Coleman SW, Jones AG. 2011. Patterns of multiple paternity and maternity in fishes. The Linnean Society of London, Biological Journal of the Linnean Society 103:735-760.
Daly-Engel T, Grubbs R, Feldheim K, Bowen B, Toonen R. 2010. Is multiple mating beneficial or unavoidable? Low multiple paternity and genetic diversity in the shortspine spurdog Squalus mitsukurii. Mar Ecol Prog Ser 403:255–267.
DiBattista JD, Feldheim K, Gruber SH, Hendry AP. 2008. Are indirect genetic benefits associated with polyandry? Testing predictions in a natural populations of lemon sharks. Molecular ecology 17:783-795.
Ebert DA , Smith WD, Cailliet GM. 2008. Reproductive biology of two commercially exploited skates, Raja binoculata and R. rhina, in the western Gulf of Alaska. Fisheries Research 94:48–57.
Ebert DA, Davis CD. 2007. Descriptions of skate egg cases (Chondrichthyes: Rajiformes: Rajoidei) from the eastern North Pacific. Zootaxa 1393:1–18.
Hitz CR. 1964. Observations on Egg Cases of the Big Skate (Raja binoculata, Girard) Found in Oregon Coastal Waters. Journal of the Fisheries Research Board of Canada 21(4): 851-854.
James KC, Ebert DA, Natanson LJ, Cailliet GM. 2014. Age and growth characteristics of the Starry Skate, Raja stellulata, with a decription of life history and habitat trends of the central California, U.S.A., skate assemblage. Environ Biol Fish 97: 435-448.
Larson S, Christiansen J, Griffing D, Ashe J, Lowry D, Andrews K. 2010. Relatedness and polyandry of Sixgill sharks, Hexanchus griseus, in an urban estuary. Conservation Genetics 12:679–690.
Sugg DW, Cheeser RK. 1994. Effective Population Sizes with Multiple Paternity. Genetics of Society of America. 137:1147-1155.
Winton MV, Natason LJ, Kneebone J, Cailliet GM, Ebert DA. 2013. Life History of Bathraja trachura from the eastern Bering Sea, with evidence of latitudinal variation in a deep-sea skate species. Journal of the Marine Biological Association of the United Kingdom: 1-12. doi: 10.1017/s00253154130001525