David W. Pfennig
Spadefoot toad (Scaphiopus bombifrons) tadpoles can develop into either a smaller, omnivorous morph or into a much larger, carnivorous “cannibal morph” that feeds on smaller conspecifics. While research on Southern spadefoot toads (Scaphiopus multiplicatus) reveals that the relative frequency of the two larval morphs reaches an equilibrium determined by both the abundance of food and the likelihood that the pond in which the tadpoles develop will persist, cannibals avoid compromising their inclusive fitness by showing kin-differential behavior. Cannibals discriminate kin from nonkin, preferentially associating with non-siblings, and more often releasing siblings unharmed, but ingesting non-siblings where those are sampled.
FURTHER READING: Lee A. Dugatkin, Principles of Animal Behavior, 3rd ed. (New York: W. W. Norton, 2013), chap. 9, “Kinship.” D. W. Pfennig, H. K. Reeve, and P. W. Sherman, “Kin recognition and cannibalism in spadefoot toads,” Animal Behaviour 46 (1993), pp. 87–94.
Video © Tom Wenseleers
While eusocial insect colonies are characterized by extensive cooperation among nestmates, they also are marked by conflict over reproduction, as workers lay haploid eggs destined to become males. Dilution of the coefficient of relatedness among workers, which results from multiple insemination of queens, can lead to worker policing of worker reproduction by nestmates that allow only closely related offspring to be reared. Furthermore, since the queen’s reproductive interests are best served by having workers invest in her offspring, eusocial insect queens actively police worker reproduction. Here, a red wasp (Vespula rufa) worker lays an egg, which is subsequently detected and eaten by the colony’s queen, who then lays her own egg in the newly vacated brood cell.
FURTHER READING: Lee A. Dugatkin, Principles of Animal Behavior, 3rd ed. (New York: W. W. Norton, 2013), chap. 9, “Kinship”; chap. 15, “Aggression.” F. L. W. Ratnieks and T. Wenseleers, “Altruism in insect societies and beyond: Voluntary or enforced?” Trends in Ecology and Evolution 23 (2008), pp. 45–52.
Frank R. Castelli; Linda S. Rayor Lab, Cornell University
The whip spiders, and in particular Phrynus marginemaculatus and Damon diadema, are among the few spiders that have been reported to exhibit social behavior. During courtship, males deposit stalked spermatophores on the ground bearing sperm masses at their tip. They then guide females over these with their pedipalps, and upon collection of these sperm masses, the female deposits the newly fertilized eggs into a brood sac beneath her abdomen. As young hatch, they climb onto their mother’s back, as shown in the stills within the present video compilation, where they undergo multiple moults toward adulthood. Young, however, preferentially aggregate with siblings when placed in an unfamiliar environment, demonstrating their ability to discriminate kin from nonkin.
FURTHER READING: Lee A. Dugatkin, Principles of Animal Behavior, 3rd ed. (New York: Norton, 2013), Chap. 9, “Kinship.” L. S. Rayor & L. A. Taylor, Social behavior in Amblypygids, and a reassessment of Arachnid social patterns, The Journal of Arachnology 34 (2006), pp. 399–421.