When should cuckolded males care for extra-pair offspring?

In socially monogamous species with bi-parental care, males suffer reduced reproductive success if their mate engages in extra-pair copulations (EPCs). One might therefore expect that males should refuse to care for a brood if they can detect that an EPC has occurred. Here, we use a game-theory model to study male brood care in the face of EPCs in a cooperatively breeding species in which offspring help to raise their (half-) siblings in their parents' next breeding attempt. We show that under certain conditions males are selected to care even for broods completely unrelated to themselves. This counterintuitive result arises through a form of pseudo-reciprocity, whereby surviving extra-pair offspring, when helping to rear their younger half-siblings, can more than compensate for the cost incurred by the male that raised them. We argue that similar effects may not be limited to cooperative breeders, but may arise in various contexts in which cooperation between (half-) siblings occurs.

Brooding fathers, not siblings, take up nutrients from embryos

It is well known that many animals with placenta-like structures provide their embryos with nutrients and oxygen. However, we demonstrate here that nutrients can pass the other way, from embryos to the parent. The study was done on a pipefish, Syngnathus typhle , in which males brood fertilized eggs in a brood pouch for several weeks. Earlier research has found a reduction of embryo numbers during the brooding period, but the fate of the nutrients from these ‘reduced’ embryos has been unknown. In this study, we considered whether (i) the brooding male absorbs the nutrients, (ii) siblings absorb them, or (iii) a combination of both. Males were mated to two sets of females, one of which had radioactively labelled eggs (using 14 C-labelled amino acids), such that approximately half the eggs in the brood pouch were labelled. This allowed us to trace nutrient uptake from these embryos. We detected that 14 C-labelled amino acids were transferred to the male brood pouch, liver and muscle tissue. However, we did not detect any significant 14 C-labelled amino-acid absorption by the non-labelled half-siblings in the brood pouch. Thus, we show, to our knowledge, for the first time, that males absorb nutrients derived from embryos through their paternal brood pouch.

Nepotism and brood reliability in the suppression of worker reproduction in the eusocial Hymenoptera

In many eusocial Hymenoptera, workers prevent each other from producing male offspring by destroying worker-laid eggs. Kin selection theory predicts that such ‘worker policing’ behaviour can evolve by increasing the average relatedness between workers and their male brood. Alternatively, if worker-laid eggs are of low relative viability, their replacement would increase the developmental reliability of the brood. Less colony investment in terms of time and resources would be lost on poor males. This gain is independent of the relatedness of the males. Unfortunately, both nepotistic and group efficiency benefits can simultaneously accrue with the replacement of worker-laid eggs. Therefore, worker behaviour towards eggs cannot completely resolve whether both processes have been equally evolutionarily important. Adequate resolution requires the presentation of worker-produced brood of various ages. The stage at which brood are replaced can discriminate whether worker policing occurs owing to a preference for closer genetic kin, a preference for the more reliable brood or both.