Parental Behavior PDF

Parental behavior FIGURE 11.1 An honest signal of condition?  Socially monogamous species are typically characterized by pair bonds that extend into the breeding season to permit biparental care of offspring, as we’ve observed in songbirds.  Polygynous species show fleeting interactions...

Parental behavior FIGURE 11.1 An honest signal of condition?  Socially monogamous species are typically characterized by pair bonds that extend into the breeding season to permit biparental care of offspring, as we’ve observed in songbirds.  Polygynous species show fleeting interactions between the sexes and the female generally cares for young  Promiscuous mating systems often occur with NO parental care.  So, what is the usefulness or benefit of caring??  There is increased survival of young to an age where they can reproduce.  BUT, how much time and energy should be invested by parents? There is limited time and energy to invest in any given offspring. So the parent makes choices as to whom to care for, and how much care to provide. The color of the mouth gape affects the amount of food that nestling barn swallows are given by their parents The effect of orange feather ornaments of baby coots on parental care Baby coots have orange feathers on their head and throat. What is the function of these orange feathers? cut off tips so chicks look black or left chicks orange (unaltered chick) Chicks reared in all orange or all black control broods showed no difference in feeding rate or growth rate. Orange chicks reared in mixed experimental broods were fed more and grew faster than black chicks in mixed broods. Adjustment of investment in sons and daughters by the red mason bee When female red mason bees are young (at the start of the breeding season), their provisioning efficiency is high, and under these conditions, the sex ratio of their offspring is biased toward daughters Small sons are produced later, when the females are older and their efficiency in filling their brood cells is low. So here we have a parent’s health determining the sex of their offspring. Local competition and local enhancement hypothesis  Local competition hypothesis When related individuals compete for mates or resources, sex ratios can become skewed because one sex is more costly to produce.  Local enhancement hypothesis On the other hand, one sex might be cheaper to produce because it provides resources or enhances the mating success of its relatives.  Ex: Seychelles warbler is a cooperative breeder  Females are the primary helping sex and males are the primary dispersing sex.  In low-quality territories where food is scarce, parents produce male offspring which are likely to disperse  In high-quality territories, parents produce female offspring that remain in the territory as helpers. Family conflict  Siblicidal behavior is tolerated by the parents under certain circumstances. Nazca booby  May have evolved because the winner of the sibling conflict has eliminated competition for food ex. Nazca booby parents permit siblicide (obligate siblicide) Compared to Blue-footed bobby parents, less likely to engage in siblicide and occurs later in the breeding season (facultative siblicide) Nazca chicks given to blue-footed parents: The foster parents can prevent killing Blue-footed chicks given to Nazca parents: Older chick often kills the young chick. So why do Nazca booby parents lay two eggs, if the younger chick is almost always killed? Blue-footed booby Reproductive insurance hypothesis: mothers in a siblicidal species lay a second egg as wikimedia.org/wikipedia/commons/1/13/Blue- insurance against hatching failure. footed_booby_2018_at_Galapagos_Islands.jpg Parental care has fitness costs and benefits Individuals must balance the survival and reproductive costs and benefits of its parental care duties Parental care has fitness costs and benefits Parents should adjust the provisioning rate they provide in accordance with 2 factors: 1. Nature of the predator (whether it consumes adults OR nestlings) 2. Annual mortality rate for breeding adults (are they short-lived (N American) or long lived (S American) They played a recording of a nest predator (in both cases a type of jay) to American robins (N A) and thrushes (S A) Both robin and thrush reduced visits to the nest for a while [the jays can find nests by watching where parent birds go]. Robins curtailed activity around the nest to a greater extent because the shorter-lived adult robins had more to gain by protecting their current brood] Then, the researchers repeated the experiment, but now exposed the parents to predators of adults. The rate at which adults fed offspring fell more sharply in South American (long-lived) birds, because the parents could live to raise another brood rather than risk their lives. Sexual conflict and parental care  What are the costs and benefits to each sex of being parental?  When the interests of mother and fathers are dissimilar, then which sex takes care of the young becomes a source of conflict between the parents.  Costs of maternal care?  Ex: European earwig female stays with clutches of eggs  Larval offspring benefit from feeding by the female (BENEFIT of REMAINING)  However, the interval between clutches is 1 week longer for the female that remains with her eggs vs. a female that leaves) (COST of REMAINING)  Costs of paternal care?  The average benefit to a male being paternal is reduced if some of the offspring were fathered by other males (COST of REMAINING)  Paternity assurance hypothesis: males are most likely to provide care when they are certain to be the father of those offspring. Paternity assurance hypothesis Territorial male bluegill sunfish are parental. They guard eggs and fry (baby fish) Some males were exposed to a sneaker fish (in a jar near the spawning male) Others males were permitted to spawn without exposure to the sneaker male. When a fish that preys upon eggs and fry is presented to the territorial male, he defends fry but not eggs. Why would they protect fry but not eggs? Evolution of mouthbrooding Interspecific and specialist brood parasitism  Obligate brood parasites always lay their eggs in the nests of other species of birds (referred to as host parent)  So – the cuckoo nestling is reared by the host parent  How does the cuckoo fool the host parent so completely? Brood parasitism  Cuckoos are extraordinary code breakers  Code breakers present the exploited species’ releaser cues to elicit a fixed action pattern  Co-evolution occurs when species interact in ways that affects the fitness of each other’s members. It’s a war!!  Co-evolutionary arms race A cuckoo baby in the nest is not just another mouth to feed. https://www.youtube.com/watch?v=SO1WccH2_YM Cuckoos  The newly hatched cuckoo baby ejects eggs or chicks of the host species – killing them.  This is a transient ontogenetic adaptation: the behavior occurs immediately after the cuckoo has hatched and disappears when all the eggs or chicks have been killed. Doing this is a major benefit to the cuckoos’ reproductive success (chance of surviving – therefore it’s an adaptation). Cuckoos  The cuckoo baby prolongs its gape to avoid injuring its foster parent – which would be easy to do considering how large the “baby” grows  Prolongation of the gape is another transient ontogenetic adaptation shown by cuckoos  After 3 weeks or so, the cuckoo leaves the next (which it has outgrown), and the foster parents keep feeding it, often having to perch on the chick’s back to drop insects into the gaping beak. Cuckoos  The cuckoo and its host engage in an co-evolutionary arms race.  Co-evolutionary arms race: When two parties in conflict exert reciprocal selective pressures on each other, with an adaptive advance made by one often leading eventually to an adaptive counter-response by the other  There are selective pressures on the host species to have mechanisms to detect the cuckoo (but at what possible cost?)  And the cuckoo responds by perfecting its ability to avoid detection  Cuckoos display egg mimicry, gape mimicry, and begging behavior mimicry Cuckoos  Egg mimicry: evolved in response to egg discrimination by the host Black arrows indicate the cuckoo’s egg  https://whyevolutionistrue.com/2011/03/04/ mimicry-the-nefarious-cuckoo/ Cuckoos  Gape mimicry: cuckoo chicks also have mouth linings that resemble that of their host  The graphs on the right side of the figure show the reflectance at various wavelengths for 3 different cuckoo species and their host.  The mouth linings of chicks trigger feeding by parents and so the host parent feeds the cuckoo chick. Multimodal mimicry of grassfinch hosts by parasitic Vidua finch nestlings The common cuckoo chick’s begging call matches that of four baby reed warblers  Sound spectrograph B shows the call of a single reed warbler chick.  Sound spectrograph C shows the call of a brood of 4 reed warbler chicks  Sound spectrograph D shows the call of a SINGLE CUCKOO CHICK Cuckoo chick’s begging calls Similarly, the begging call of Horsfield’s bronze cuckoo (a specialist brood parasite on superb fairy-wrens) resembles that of an entire brood of superb fairy wren chicks The shining bronze cuckoo rarely parasitizes superb fairy wren nests and they do not look like superb fairy wren chicks and they do not produce a facsimile of their begging calls. Begging mimicry: a coevolutionary arms race?  What countermeasures have evolved in the parasitized host?  Superb fairy wren mothers sing to their unhatched eggs and teach the embryos a “password” or a single note – that they must sing to get fed.  The male is also taught this note.  Chicks unable to produce this note while begging do not get fed.  User:benjamint444, CC BY-SA 3.0 , via Wikimedia Commons More cuckoo trickery Horsfield’s hawk cuckoo parasitizes the bush robin. Bush robins nest close to the ground, where there is more danger of predation if chicks make a lot of noise. The cuckoo chick simulates a nest full of chicks by waving its orange “elbow patch”, making it look like another chick. Cowbirds  Sometimes, it is more beneficial for the host to accept the parasitic egg rather than remove it.  Ex: brown-headed cowbird parasitizes warblers. Unlike cuckoo eggs, cowbrid eggs do NOT resemble their hosts’ eggs. Brown-headed cowbird Cowbird eggs in indigo bunting next  Choices for a parasitized host:  Accept the parasitic egg or  Abandon the clutch  Abandonment can have severe consequences  Mafia hypothesis: hosts often accept the parasitic egg out of fear of retaliation. The cowbird will destroy the host’s nest if the egg is rejected. If the host rebuilds the nest and lays another clutch, the avenging cowbird will destroy that one as well.  cowbird to host: I will make you an offer you can’t refuse… The size of an experimental “brood parasite” nestling relative to its host species determines its survival chances. This undoubtedly played a role in the evolution of parasitism. Evolution of brood parasitism Conclusions  Parents invest differently in their offspring [mom always liked you best]  Parental care can be delivered by the mother, by the father, or by both.  Parents not only favor some offspring over others, they may manipulate the sex of their progeny for the parent’s maximum benefit.  Parents in some species of bird show complete indifference and allow siblicide.  Which sex provides care depends on the relative costs/benefits of caring – who has the most to lose if they provide care?  Parents are likely to recognize their young in colonial breeding situations, and are much less likely to do so in non=colonial situations.  Finally, in the case of brood parasitism, neither parent provides the care; the offspring is raised by another species. How this evolved is as of yet unclear.