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On the Origin of Parental Care and the Early Evolution of Male and Female Parental Roles in Birds

Tomasz Wesolowski
The American Naturalist
Vol. 143, No. 1 (Jan., 1994), pp. 39-58
Stable URL: http://www.jstor.org/stable/2462853
Page Count: 20
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On the Origin of Parental Care and the Early Evolution of Male and Female Parental Roles in Birds
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Abstract

In over 90% of bird species both parents participate in care of eggs and young. The reasons for this unique phenomenon are not adequately understood. The comparative approach shows that in Eoaves, the most primitive of extant birds, paternal care constituted the ancestral state. As uniparental paternal care is unknown in reptiles, most probably it had to be derived from the state of absence of care. Thus, the lineage of reptiles without postovipositional attendance of eggs constitutes a point of departure. I address two main questions: how avian care could have evolved from such a state, and how male and female parental roles have been shaped. I propose that the evolution proceeded initially through stages without parental care (main adaptations to flight appeared then) but with increasing investment in eggs, resulting in the appearance of sequential ovulation and of very large eggs producing superprecocial young able to fly shortly after hatching. I suggest that parental care appeared only at that stage. Because of much lower costs it developed in males: the males could combine care and mate attraction via territoriality, whereas tending to eggs-very costly for females-would substantially decrease their fecundity. In the beginning, parental care consisted of egg guarding; incubation developed later. Initially, sets of eggs to be incubated were probably laid by several females; in this way some level of hatching synchronization sufficient to permit the appearance of posthatching care could be achieved. When care for young developed, egg size could start to decrease, and an avenue toward altricial development was opened. Properties of eggs were coevolving with parental care, which made them more dependent on care. When eggs could no longer develop without the presence of a parent, parental care became fixed. I propose that biparental care originated then, when parental care was already obligatory and environmental conditions demanded the constant presence of a parent. This could be accomplished only by the participation of two birds replacing one another on the nest. Such selective pressure would lead to the formation of biparental care with identical roles, the system of care prevailing among living birds. This system could be further transformed to biparental care with role specialization, uniparental double clutching, or, via the reduction of participation of one sex, either to maternal care or to the reappearance of paternal care.

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