EFFECTS OF MALE GENETIC CONTRIBUTION AND PATERNAL INVESTMENT TO EGG AND HATCHLING SIZE IN THE CRICKET, GRYLLUS-FIRMUS

Egg provisions represent the complete energy supply of oviparous organ isms from fertilization until hatching, and egg size is generally corr elated with initial offspring size and a suite of other early fitness related traits. Since egg size is determined by the mother, little att ention has been given to potential sources of paternal effects on eith er egg size or initial offspring size. This study considers two proces ses by which the sire can affect the egg size and/or initial body size of his offspring, in the multiply mated cricket, Gryllus firmus. The first is a paternal genetic effect, whereby differences in offspring g enotype result in differences in the efficiency of metabolising availa ble resources. The second is a paternal environmental effect, whereby the quality or size of paternal investment varies among male phenotype s and this is correlated with the size of eggs the females subsequentl y produce. Using a one-locus two-allele recessive mutation for pale ey e colour as a marker, a mating experiment was designed which enabled t he discrimination between eggs fertilized by two males mated simultane ously to a single female. The results of this experiment suggest that sire effects on egg and initial body size occur through both processes . Eggs fertilised by the two males were significantly different at day ten of development, suggesting that the genetic contribution of the s ire is affecting embryonic body size. Further, a negative correlation was found between the head size of the pale eyed male and the size of all the eggs that the female laid, suggesting an effect of male size o f the amount of nutrients the female receives from her mates. The resu lts of this study suggest that paternal effects may be both more commo n and more profound than previously thought, and that studies examinin g early fitness traits that are correlated to egg size or initial body size, in oviparous animals, should consider the possibility and impor tance of the paternal contribution.