EXAMINATION OF SPERMATOPHORE PRODUCTION BY LABORATORY‐MAINTAINED LOBSTERS (Homarus)

Abstract

Lobster aquaculture requires control of reproductive processes. We have previously described an electrical stimulation technique for collecting spermatophores from living lobsters (Homarus americanus). These spermatophores can potentially be used in a variety of ways including: 1) experimental manipulation of sperm, 2) artificial insemination of females, 3) sperm banking, and 4) evaluation of sperm production by the male. In this study, we evaluated spermatophore production and extrusion from: 1) laboratory reared H. americanus and H. gammarus, 2) stressed, wild‐caught H. americanus, and 3) laboratory bred and reared hybrid males from reciprocal interspecific crosses. Our results show that the extrusion technique can be used successfully on H. americanus, H. gammarus and hybrid males. Laboratory reared H. americanus and H. gammarus from both Aquaculture Enterprises and Bodega Marine Laboratory extruded spermatophores in 60–85% of all trials. The majority of these spermatophores were of high quality containing large sperm masses with morphologically normal sperm. Stressed H. americanus, obtained from a market in Sunset Beach, California, 24 hours after shipment from New England, extruded fewer spermatophores which were shorter in length and inferior in quality. Hybrid males extruded spermatophores possessing a morphologically normal wall, but lacking sperm. These results demonstrate that this electrical stimulation technique can be used to screen males for spermatophore production and identify certain types of infertility.

Crossing the pond: genetic assignment detects lobster hybridisation

“…Currently, it is difficult to ascertain the threat posed to European lobster stocks from hybridisation with H. americanus, since conflicting information exists as to both the likelihood of interspecific mating and the fertility of resultant hybrids. Talbot et al 21 found that the spermatophores of captive-reared hybrid males lacked sperm, suggesting that they were infertile, but Kitaka (pers comm., as cited by 22 ) achieved interspecific mating in captivity and asserted that both sexes of the resultant hybrid offspring were fertile. Fertile hybrids enable backcrossing and pervasive population-level introgression, although hybridisation is still a conservation threat even where hybrids are infertile, since it represents wasted reproductive effort 5,6 .…”

“…Although concerns that pathogenic syndromes of H. americanus may spread to devastate H. gammarus stocks have been tempered by the latter's apparent disease resilience 18,19 , fears that American lobster introductions may impact European populations through competition and genetic introgression have not been so readily mitigated, particularly following recent observations that Americans both predate on and interbreed with European counterparts 20 . Reports of wild hybridisation are concerning as well as surprising; while long established that Homarus hybrids could be bred in captivity through induced fertilisation 21 , it was also proposed that behavioural characteristics of sexual selection should constrain interspecific mating in the wild 22 . However, this appears not to be the case 20 .…”

Comparison of genetic and morphological methods to detect the presence of American lobsters, Homarus americanus H. Milne Edwards, 1837 (Astacidea: Nephropidae) in Norwegian waters

“…The most successful crossings appear to be American male with European female. The pure strains and produced hybrids have been used in numerous other experiments related to survival, growth, aggression, oxygen binding, egg quality etc (Gruffydd et al, 1975;Anon, 1978;Carlberg et al, 1978Carlberg et al, , 1979Mickelsen et al, 1978;Talbot et al, 1983Talbot et al, , 1984Harper & Talbot, 1984;Zalgalcky, 1985;Zalgalcky & Tidmarsh, 1985). The overall conclusion from several of these studies is that hybrid progeny show intermediate traits, rather than dominance of one parental type.…”

Interspecific hybridization of decapod crustacean species with commercial interest—A review

“…120 Hybrid males of H. americanus and H. gammarus were able to extrude spermatophore (about 71-80%) using an extrusion technique with electrical stimulation, but the spermatophore lacked sperm despite having a morphologically normal wall (a white sperm mass was not visible in any of the hybrid spermatophore examined microscopically) and the hybrid females may produce fertile eggs if back-crossed. 127 In hybridization H. gammarus  H. americanus, pure breed and hybrid offspring reached the post-larval stage in approximately the same time but the larvae of H. gammarus and hybrids were larger than those of H. americanus. A 1-year comparison of growth and survival revealed no significant differences in the size attained by juveniles of the two lobster species or their hybrids.…”

“…The findings suggest that European lobsters can recognize conspecific mates, possibly through chemical signals, and that these signals act as pre‐mating barriers, preventing hybridization 120 . Hybrid males of H. americanus and H. gammarus were able to extrude spermatophore (about 71–80%) using an extrusion technique with electrical stimulation, but the spermatophore lacked sperm despite having a morphologically normal wall (a white sperm mass was not visible in any of the hybrid spermatophore examined microscopically) and the hybrid females may produce fertile eggs if back‐crossed 127 . In hybridization H. gammarus × H. americanus , pure breed and hybrid offspring reached the post‐larval stage in approximately the same time but the larvae of H. gammarus and hybrids were larger than those of H. americanus .…”