title: Fertilisation and early developmental barriers to hybridisation in field crickets.
abstract: BACKGROUND
  Post-mating interactions between the reproductive traits and gametes of mating individuals and among their genes within zygotes are invariably complex, providing multiple opportunities for reproduction to go awry. These interactions have the potential to act as barriers to gene flow between species, and may be important in the process of speciation. There are multiple post-mating barriers to interbreeding between the hybridising field crickets Gryllus bimaculatus and G. campestris. Female G. bimaculatus preferentially store sperm from conspecific males when mated to both conspecific and heterospecific partners. Additionally, conspecific males sire an even greater proportion of offspring than would be predicted from their sperm's representation in the spermatheca. The nature of these post-sperm-storage barriers to hybridisation are unknown. We use a fluorescent staining technique to determine whether barriers occur prior to, or during embryo development.
  
  
  RESULTS
  We show that eggs laid by G. bimaculatus females mated to G. campestris males are less likely to begin embryogenesis than eggs from conspecific mating pairs. Of the eggs that are successfully fertilised and start to develop, those from heterospecific mating pairs are more likely to arrest early, prior to blastoderm formation. We find evidence for bimodal variation among egg clutches in the number of developing embryos that subsequently arrest, indicating that there is genetic variation for incompatibility between mating individuals. In contrast to the pattern of early embryonic mortality, those hybrids reaching advanced stages of embryogenesis have survival rates equal to that of embryos from conspecific mating pairs.
  
  
  CONCLUSIONS
  Post-sperm-storage barriers to hybridisation show evidence of genetic polymorphism. They are sufficiently large, that if the species interbreed where they are sympatric, these barriers could play a role in the maintenance of reproductive isolation between them. The number of eggs that fail to develop represents a substantial cost of hybridization to G. bimaculatus females, and this cost could reinforce the evolution of barriers occurring earlier in the reproductive process.
authors: Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Cornwall Campus, Penryn, Cornwall, UK.
authors: Frances
authors: F
authors: Tyler
authors: Rolando
authors: R
authors: Rodríguez-Muñoz
authors: Tom
authors: T
authors: Tregenza
mesh_terms: D000818:Animals; D047108:Embryonic Development; D005260:Female; D005306:Fertilization; D049810:Genetic Speciation; D006135:Gryllidae / Q000145:classification* / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D006824:Hybridization, Genetic; D008297:Male; D010063:Ovum / Q000502:physiology; D060047:Reproductive Isolation; D013094:Spermatozoa / Q000502:physiology