Non-kin cooperation in bats

Abstract

One contribution of 18 to a theme issue 'The evolution of cooperation based on direct fitness benefits'. Many bats are extremely social. In some cases, individuals remain together for years or even decades and engage in mutually beneficial behaviours among non-related individuals. Here, we summarize ways in which unrelated bats cooperate while roosting, foraging, feeding or caring for offspring. For each situation, we ask if cooperation involves an investment, and if so, what mechanisms might ensure a return. While some cooperative outcomes are likely a by-product of selfish behaviour as they are in many other vertebrates, we explain how cooperative investments can occur in several situations and are particularly evident in food sharing among common vampire bats (Desmodus rotundus) and alloparental care by greater spear-nosed bats (Phyllostomus hastatus). Fieldwork and experiments on vampire bats indicate that sharing blood with non-kin expands the number of possible donors beyond kin and promotes reciprocal help by strengthening long-term social bonds. Similarly, more than 25 years of recapture data and field observations of greater spearnosed bats reveal multiple cooperative investments occurring within stable groups of non-kin. These studies illustrate how bats can serve as models for understanding how cooperation is regulated in social vertebrates.

Correlated pay-offs are key to cooperation

“…Reciprocity, the third potential cause of correlated pay-offs, is arguably the most contended possibility to generate cooperation and altruism [12,32]. It is the theme of this article and a focus of many contributions to this special issue of the Philosophical Transactions [7,[33][34][35][36][37].…”

“…Such conditions are unlikely to be widespread in nature [34]. However, the rule 'help someone who has helped you before' can be selected under a much wider range of conditions, for instance involving individual relationships such as partnerships and friendships [7,[162][163][164], and contingency may be based on the integration of several interactions over longer timespans (attitudinal reciprocity [165]). If exchanges of different commodities are considered as well [136], the power of this mechanism emerges even more clearly (see [166] for a discussion of underlying mechanisms).…”

“…(2) The prediction that high benefits must be gained by receivers in reciprocal cooperation has been confirmed by the mutual blood donations provided by vampire bats, which face a high starvation risk owing to their small body size [7,104]. Blood is donated to related and unrelated individuals, but experiments have revealed that food received from a social partner in a previous interaction predicts food donations by roughly an order of magnitude better than relatedness [105].…”

“…Regarding fitness consequences of reciprocal food sharing, important effects have been suggested for vampire bats [7,104,105], where the benefit of receiving a blood donation are typically much higher than the costs of providing it owing to the inevitable threat of starving to death when not obtaining a blood meal within a maximum period of 70 h [104,191]. Such asymmetries between costs of provided and benefits of received help can immensely enhance the evolutionary stability of reciprocity, which may explain also the condition-dependent help rats provide to hungry partners [111].…”

“…[2][3][4][5]; cf. [6,7]), and by the realization that cooperative interactions among non-relatives are widespread in contexts outside of cooperative breeding (e.g. [8][9][10][11]).…”