Combination of seven surveys of blood parasites in North American passerines reveals weak, highly significant association over species between incidence of chronic blood infections (five genera of protozoa and one nematode) and striking display (three characters: male "brightness," female "brightness," and male song). This result conforms to a model of sexual selection in which (i) coadaptational cycles of host and parasites generate consistently positive offspring-on-parent regression of fitness, and (ii) animals choose mates for genetic disease resistance by scrutiny of characters whose full expression is dependent on health and vigor.

http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Hamilton1982.pdf

Heritable true fitness and bright birds: a role for parasites?

It has been argued that females should be able to choose parasite-resistant mates on the basis of the quality of male secondary sexual characters and that such signals must be costly handicaps in order to evolve. To a large extent, handicap hypotheses have relied on energetic explanations for these costs. Here, we have presented a phenomenological model, operating on an intraspecific level, which views the cost of secondary sexual development from an endocrinological perspective. The primary androgenic hormone, testosterone, has a dualistic effect; it stimulates development of characteristics used in sexual selection while reducing immu- nocompetence. This "double-edged sword" creates a physiological trade-off that influences and is influenced by parasite burden. We propose a negative-feedback loop between signal intensity and parasite burden by suggesting that testosterone-dependent signal intensity is a plastic re- sponse. This response is modified in accordance with the competing demands of the potential costs of parasite infection versus that of increased reproductive success afforded by exaggerated signals. We clarify how this trade-off is intimately involved in the evolution of secondary sexual characteristics and how it may explain some of the equivocal empirical results that have surfaced in attempts to quantify parasite's effect on sexual selection.

Parasites, bright males, and the immunocompetence handicap

Theoretical studies of life history evolution almost unanimously incorporate some form of tradeoff between life history variables, such as reduced parental survival due to increased reproductive effort. These tradeoffs, or costs of reproduction, are fundamental in predicting the optimal life history in any given environment. The importance of such costs in theoretical models has motivated researchers to check that they exist by seeking an association between some component of reproductive effort, such as fecundity, and some form of cost, such as parental survival. Four methods have been used for making these evaluations: 1) Phenotypic correlations, where some index of reproductive effort is correlated with a potential cost, 2) Experimental manipulations, where reproduction is directly manipulated and a cost-related response is measured, 3) Genetic correlations, where formal quantitative genetic designs are used to estimate the genetic correlation between some component of reproductive effort and some component of cost, and 4) Correlated responses to selection, where artificial selection causes correlated changes in reproductive effort and some component of costs. Because the theoretical studies are models of evolution, I argue that a relevant empirical study must deal with genetically based tradeoffs. By this criterion, only the last two methods (which represent a small minority of the reviewed studies) properly address the "costs" dealt with by theoreticians; however, this evaluation is not intended as a litmus test for the merits of a given approach to the problem. I discuss both the important contributions of the first two methods to our understanding of the costs of reproduction and the limitations of the last two methods in assessing "costs".

Costs of reproduction: an evaluation of the empirical evidence

Body mass in comparative primatology

Infanticide among animals: A review, classification, and examination of the implications for the reproductive strategies of females

At maturity, female baboons in the Amboseli National Park of Kenya generally attain a rank position among adults near to that of their mothers. However, the age of a female9s mother and the difference in ages between sisters also influence the rank acquisition process. These latter demographic variables, which are sensitive to changes in resource availability, may account for the close association both within and among primate species of specific patterns of rank organization and specific environmental conditions.

Long-Term Consistency of Dominance Relations Among Female Baboons (Papio cynocephalus).

Longitudinal data from a population of yellow baboons,Papio cynocephalus, in the Amboseli National Park, Kenya, provide life history parameter estimates. Females reached menarche at approximately four-and-a-half years of age and then cycled for approximately a year before first conception. Postpartum anestrum averaged 12 months but ranged from six to 16 months. In cases of still births or infant death during postpartum amenorrhea, females commenced cycling after approximately one month. In mature females the time spent cycling before conception was five months on the average with a range from one to over 18 months. Only half of all full-term pregnancies resulted in infants who survived the first year of life; only a third, in infants who survived until the birth of their mother’s next infant. In comparison with data from laboratory colonies, our data indicate that female baboons in Amboseli are older at birth of first infant. They have, on the average, a somewhat shorter interbirth interval than was estimated from earlier crossectional field data, and therefore spend a larger portion of their adult life pregnant, but have a much longer interval—at least three years on the average—between the birth of an infant and the birth of that infant’s next older surviving sibling. A number of morphological changes in immature baboons are described.

/pdf/life-history-of-yellow-baboons-physical-development-1t6pgzdk84.pdf

Life History of Yellow Baboons: Physical Development, Reproductive Parameters, and Infant Mortality

The primary locus of contact between free-living yellow baboons (Papio cynocephalus) in the Amboseli National Park of Kenya and the infective stages of their intestinal parasites is believed to be soil beneath sleeping trees contaminated by the baboons' own fecal emissions. In this report, we present evidence both that infective ova and larvae of intestinal parasites are found at very high densities in the soil beneath sleeping groves and that Amboseli baboons substantially reduce their contact with this reservoir of parasites by alternating periods of a few consecutive nights' use of any particular grove with much longer periods of avoidance of that grove. Although many factors other than the presence of parasite larvae also influence choice of sleeping groves, we propose as a working hypothesis that the temporal pattern of sleeping grove alternation shown by Amboseli baboons reflects a subtle behavioral strategy for parasite avoidance.

/pdf/alternation-of-sleeping-groves-by-yellow-baboons-papio-34bap4kbxm.pdf

Alternation of sleeping groves by yellow baboons (Papio cynocephalus) as a strategy for parasite avoidance

Female savanna baboons (Papio cynocephalus) had a longer postpartum amenorrhea and thereafter cycled longer before conceiving if their previous infant survived than if that infant died. Among mothers of surviving infants, differences in maternal care produced differences in age of weaning and age of independence but did not result in differences in interbirth intervals.

http://science.sciencemag.org/content/sci/201/4360/1028.full.pdf

Primate infant's effects on mother's future reproduction

In a longitudinal study of individually identified wild baboons in Amboseli National Park, Kenya, we collected data on physical development and reproductive maturation. Confirming and extending our earlier results, we demonstrated that the ratio of ages at which developmental milestones occur in the field as compared to those under extensive provisioning or in captivity were approximately 5:3. The age range for some developmental milestones was quite narrow and discrete, while for others there was considerable between-individual variability and more gradual changes. For infants, only the change from pink to gray of the paracallosal skin occurred within a brief age span. For older animals two important developmental events are readily identified and occur within a fairly narrow age range: Rapid enlargement of testes at 5 to 6 years for males and onset of menarche at 4 to 5 ½ years for females. In the present report, we considered some consequences of accelerated or delayed maturation. We further explored the need to employ different age-class criteria for different research problems.

/pdf/physical-maturation-and-age-estimates-of-yellow-baboons-2iaumg5iny.pdf

Glenn Hausfater

Papers

Long-Term Consistency of Dominance Relations Among Female Baboons (Papio cynocephalus).

Life History of Yellow Baboons: Physical Development, Reproductive Parameters, and Infant Mortality

Alternation of sleeping groves by yellow baboons (Papio cynocephalus) as a strategy for parasite avoidance

Primate infant's effects on mother's future reproduction

Physical maturation and age estimates of yellow baboons, Papio cynocephalus, in Amboseli National Park, Kenya