Effects of male genetic contribution and paternal investment to egg and hatchling size in the cricket, Gryllus firmus

Abstract

AbstractEgg provisions represent the complete energy supply of oviparous organisms from fertilization until hatching, and egg size is generally correlated with initial offspring size and a suite of other early fitness related traits. Since egg size is determined by the mother, little attention has been given to potential sources of paternal effects on either egg size or initial offspring size. This study considers two processes 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 genotype result in differences in the efficiency of metabolising available resources. The second is a paternal environmental effect, whereby the quality or size of paternal investment varies among male phenotypes and this is correlated with the size of eggs the females subsequently produce. Using a one‐locus two‐allele recessive mutation for pale eye colour as a marker, a mating experiment was designed which enabled the discrimination between eggs fertilized by two males mated simultaneously 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 sire 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 of the amount of nutrients the female receives from her mates. The results of this study suggest that paternal effects may be both more common and more profound than previously thought, and that studies examining early fitness traits that are correlated to egg size or initial body size, in oviparous animals, should consider the possibility and importance of the paternal contribution.