Sociality, Mate Choice, Sexual Selection, and Breeding Systems

Resource Defensibility Brandt’s Cormorants Defend nest site on cliff Do not defend feeding sites at sea Sage grouse food is Not limited, nor defended Nest is not defended as that might increase detection by predators No defensible resource allows leks to form Food and space to breed are defensible in most songbirds, so all purpose territories evolve (Brown 1964)

Sexual Selection and Mating Systems Diversity –Polyandry, Polygyny, Polygynandry, and Monogamy Male-Male Competition and Female Choice –Multiple criteria, honest signals, good genes –Arbitrary criteria, runaway selection, exaggerated characters, linkage of genes for female preference with genes for male traits Or culture, nestlings imprint on father’s characters –Alters (bowers)

Parental Care in Dinos Male parental care is rare in animals generally, but common in birds What about dinosaurs that have been found with nests? clutch volumes much greater than in female-only caring crocs clutch volumes more closely matched to birds in which males care for young, suggesting primitive character was polygamy, specifically polyandry Log (Body mass) Other dinos archosaurs (Varricchio et al. 2009)

Evolution of Bi-parental Care Male care in dinos to bi-parental care in modern birds –Increasing egg size allowed precotial young (which could fly quickly) –Males could invest in care because female investment in egg itself was already very high Male egg guarding then incubation (less needed in tropics, mound nesters as an example today) –Female birds can only lay 1 egg at a time (1 ovary, ovulation inhibited by presence of an egg in oviduct) Better to spread them among several baskets initially (polyandry) –With parental care, egg size could decrease and more altricial young could be born and cared for Females are better off producing more but smaller eggs if they are cared for Females could benefit by reducing egg loss to predators or male abandonment by also contributing to care Favors evolution of biparental care, then perhaps specialization in distinct male female roles. (Wesolowsk 1994)

Sexual Selection and Mating Systems Polyandry –Jacana Polygyny –Typically males compete indirectly for females by defending important resources (like foraging grounds in blackbirds) or by attracting females to display grounds (like grouse leks) –Some birds defend female harems Montezuma oropendola Males defend colonies of females, alpha male rules (like elephant seal) and gets most of copulations (and pass on most genes) Females do all the nestling care –May occur in other blackbirds Cowbirds, grackles where males do not invest in parental care Clue to occurrence is sexual dimporphism and grouping behavior of females (Webster 1994)

Sexual Selection and Mating Systems Polygynandry –Smith’s Longspur Females pair and copulate with more than one male for a single clutch of eggs Males pair and copulate with two or more females Intense sperm competition due to promiscuous females Several males routinely feed a single brood Not territorial All males in a neighborhood sing SAME song –Allows males to easily recognize intruders and females to mate only with local males who will help her raise brood Briskie 1999

Monogamy Social versus Genetic Common Crossbill (Kleven et al. 2008) –Extrapair paternity seems to be common in socially monogamous passerines, but the genetic mating system of most species is currently unknown. –no evidence of extrapair paternity among 96 offspring in 34 examined broods. –Common Crossbills thus seem to represent an exception to the rule of extrapair mating among socially monogamous passerine bird species. –A potentially important selective pressure preventing promiscuity –in Common Crossbills is the harsh environmental conditions experienced during breeding at wintertime, which may increase the importance of paternal care and limit the time available for seeking extrapair copulations. (Moller and Birkhead 1993)

Tradeoffs Migration may limit resources (energy and time) available for investment in parental care and territory defense Sexual selection for parental care may reduce time and energy available for migration –Breeding systems may determine or respond to migration behavior Shorebirds: Garcia-Pena et al. 2009)

In comparison of shorebirds, it appears that migration drives parental care shift, not vice versa (Garcia-Pena et al. 2009)

Costs of Breeding Systems More male:male competition leads to increased bias toward male mortality Female-female competition does not Parental care also is costly Liker and Szekely 2005

Conservation Implications Polygyny can be costly In sage-grouse modelling study Ne was only 19% of N because of variation in reproductive success between years and the skew in breeding sex ratio Resulted in small effective population (42) which may suffer inbreeding effects (low hatchability was observed Need to manage for larger than one might expect population sizes (Stiver et al. 2008)

Conservation Implications Flexible mating systems may counteract synchronized environmental fluctuations When sex ratio becomes skewed, if polygamy can occur, then chance of extinction is reduced Lesser Spotted Woodpecker in Germany –Models suggest that when male skew in sex ratio occurs, then polyandry would reduce probability of extinction (Rossmanith et al. 2006)

Sociality Pair Territoriality Kin groups Extended Families Ephemeral Flocks Groups of Families in Permanent Flocks –Fission Fusion Colonies

Routes to Sociality (Brown 1974)

Long-tailed Manakin Alpha and beta male pairs display at leks for females Alphas get nearly all copulations How are these roles set? –Social networks early in life are important 4-5 years later (McDonald 2007)

Note how social connectivity early, not late is a key to attracting females (McDonald 2007)

Optimal Group Size General consideration of tradeoffs to sociality Sociality often reduces individual workload, fear, predation, finding unpredictable foods, etc Sociality also increases disease, competition, conspicuousness, cuckoldry You can predict the optimal group size depending on the various advantages and disadvantages

Raven Information Centers (1) Roosts comprised both knowledgeable and naive foragers. (2) Departures from roosts were highly synchronized, with most members departing in one direction. (3) Direction of departure often changed from day to day. (4) Birds made naive of food sources (by being withheld from the wild and then allowed to join roosts) followed roost-mates to new feeding sites, whereas control birds held and released outside of roosts rarely found the local food bonanzas. (5) Birds made knowledgeable of food sources (by being released at new carcasses) joined roosts and led roost-mates to the food on three of 20 occasions. (6) The same individuals switched leader and follower roles depending upon their knowledge of feeding opportunities. (Marzluff et al. 1996)

Why Recruit? Not Kin Selection Parker et al. 1994

Why Recruit? Marzluff et al Increase foraging flock to optimal Depends on if you are subordinate or dominant

Wild Turkey Myth Reality (at least in Texas Watts and Stokes 1971)

Strong Dominance Hierarchy Dominance is set, nearly permanently, in first year of male’s life Dominants mate, subordinate sibs rarely do so –Young males form sib groups that remain together for life, coalesce during winter but compete for mates on lek in spring –Females go to lek and males travel by, displaying as sib groups

Male Dominance Snood Length Matters (Buchholtz 1997)

It is Good to Be King If a turkey has a choice, it makes sure its snood is the largest in the group

Why Such Brotherly Love? Multiple displaying males may increase chance of female response Brothers share, on average, 50% of genes

Female Choice Snood Length Matters (Buchholtz 1995)

Nice Snood

References Briskie, J. V Song variation and the structure of local song dialects in the polygynandrous Smith’s Longspur. Can. J. Zool. 77: Brown, J. L The evolution of diversity in avian territorial systems The Wilson Bulletin 76: Brown, J. L Alternate routes to sociality in jays: with a theory for the evolution of altruism and communal breeding. American Zoologist 14: Garcia-Pena, G. E., Thomas, G. H., Reynolds, J. D., and T. Szekely Breeding systems, climate, and the evolution of migration in shorebirds. Behavioral Ecology 20: Kleven, O., Bjerke, B-A., and J. T Lifjekl Genetic monogamy in the Common Crossbill (Loxia curvirostra). J. Ornithology 149: Liker, A., and T. Szekely Mortality costs of sexual selection and parental care in natural populations of birds. Evolution 59: Marzluff, J. M. and B. Heinrich Foraging of vagrant common ravens in the presence and absence of territorial adults: an experimental analysis of social foraging. Animal Behavior 42: Marzluff, J. M., Heinrich, B., and C. S. Marzluff Communal roosts of common ravens are mobile information centers. Animal Behaviour. 51: McDonald, D. B Predicting fate from early connectivity in a social network. Proc. Natl. Acad. Sci 104: Moller, A. P. and T. R. Birkhead Cuckoldry and sociality: A comparative study of birds. The American Naturalist 142: Parker, P. G., Waite, T.A., Heinrich, B. and J. M. Marzluff Do common ravens share food bonanzas with kin? DNA fingerprinting evidence. Animal Behaviour.48: Rossmanith, E., Grimm, V., Blaum, N., and F. Jeltsch Behavioural flexibility in the mating system buffers population extinction: lessons from the lesser spotted woodpecker Picoides minor. J. Animal Ecology 75: Stiver, J. R., Apa, A. D., Remington, T. E., and R. M. Gibson Polygyny and female breeding failure reduce effective population size in the lekking Gunnison sage-grouse. Biological Conservation 141: Varricchio, D. J., Moore, J. R., Erickson, G. M., Norell, M. A>, Jackson, F. D., and J. J. Borkowski Avian paternal care had dinosaur origin. Science 322: (and erratum 7 Aug. 2009). Webster, M. S Female-defence polygyny in a Neotropical bird, the Montezuma oropendola. Anim. Behav. 48: Wesolowski, T On the origin of parental care and the early evolution of male and female parental roles in birds. The American Naturalist 143:39-58.