Parental Care

Cost vs. benefit of parental care Birds that are likely to live long protect themselves (have smaller clutches of eggs, know they can probably mate again). Birds that are short lived have more to gain by protecting their young because they may not get another chance. In B, the short lived robins reduced their nest visits more than the thrushes. Opposite for an adult predator.

Why maternal more than paternal? Egg investment is the obvious answer but, in many species females leave the eggs in the care of the male

Cost benefit ratio Female maternity is 100% Male paternity might be 80% If the cost of parental care is the same for both females and males in terms of energy and inability to find new mates, the ratio is clearly in the female’s favor Explains why females provide more parental care than males Costs may also NOT actually be equal

Exceptions to this rule… Male sticklebacks care for up to 10 clutches of eggs at a time, females could only do one Less cost for males Both male and female cichlids may mouth brood Also, females can’t forage while guarding eggs, so they don’t grow as big, and egg quality suffers Male parental behavior may be especially attractive to females, so benefit is greater for that reason too

Parental discrimination Mothers are very adept at picking out and caring for only their offspring even in very crowded conditions Bats, seals, rodents Why even have these communal nests? What signals might aid the discrimination?

Recognizing Kin Production Offspring produce a cue that signals their identity Perception Parents are able to detect the cue and recognize it through comparison to some reference Self-referent phenotype matching Template stored or online processing Action Parental action depends on matching outcome Affiliative, feeding, grooming, chasing, killing, etc

Auditory cues Clear species discrimination amongst closely related birds but those who nest in large colonies together have young that emit highly distinctive sounds (left), while those that nest singly sound more similar to each other. Also the baby fur seals use their distinctive calls to reunite with their mothers after weeks separation.

Other cues Olfactory/Pheromone Body Size Coloration, Patterning …

Discussion Question Occasionally, female Mexican free-tailed bats make mistakes and feed an infant that is not their biological offspring. This mistake surely would have been avoided if they nested alone. -Does this mean that the parental behavior of this species is not adaptive? -Use cost-benefit analysis to develop alternative hypotheses to account for the “mistakes”.

Adoption of genetic strangers Colonial, ground-nesting gull chicks not being fed by their parents may leave the nest and seek adoption by other parents They beg, act submissive, and usually are taken in Why? If discrimination is so important, why do parents ever adopt?

Brood Parasites Lay eggs in another species’ nest Why is it tolerated? Can’t differentiate eggs shape, size, color “Mafia” hypothesis

FIGURE 11.24  The mafia hypothesis as tested with parasitic cowbirds and prothonotary warblers.  (A) In treatment 1, a cowbird laid an egg in the nest, which was then removed by the experimenter. Subsequently, the warbler eggs in most nests in this treatment were destroyed, presumably by the thwarted cowbird. In treatment 2, all nests were parasitized but the cowbird eggs were left in the nests, which were largely untouched by predators thereafter. In treatment 3, the cowbird eggs were removed from the parasitized nests, which were then made inaccessible to cowbirds; none of these nests was harmed after removal of the parasite’s egg. (B) The warblers produced more offspring under treatments 2 and 3 than under treatment 1. Bars depict mean +/– SE. (After Hoover and Robinson 2007, © 2007 National Academy of Sciences, USA; photograph © iStock.com/ziggy7.)   FIGURE 11.24  The mafia hypothesis as tested with parasitic cowbirds and prothonotary warblers

FIGURE 11.25 Prinia produce eggs that vary in color and patterning FIGURE 11.25  Prinia produce eggs that vary in color and patterning, which influences their ability to detect and reject parasitic cuckoo finch eggs.  (A) Examples of eggs from experimental clutches and naturally parasitized nests. The images in the top three rows show the range of colors and patterns found in prinia eggs. Lines under the eggs indicate groups originating from the same clutch. The two images in the bottom row show naturally parasitized clutches with one cuckoo finch egg (left) or two cuckoo finch eggs (right). Hosts do not seem to use marking variations in egg rejection decisions. (B) Foreign eggs were more likely to be rejected the more they differed in color from the host’s own eggs. As foreign eggs increased in number, hosts required a greater difference in color to reject them. Color differences are discrimination units or “just noticeable differences” (JNDs), where a JND of less than 1 means that two objects cannot be discriminated, and values between 1 and 3 should be difficult to discriminate. Box plots show median bars and interquartile ranges; whisker lines show outer quartiles. (From Stevens et al. 2013.)