Rare ectotherm biparental care. Who cares? Determining optimal parental investment per offspring Trade offs:

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1 Rare ectotherm biparental care Burying beetles, clownfish Parent beetles bury, defend, shave, roll, inoculate carcass Determining optimal parental investment per offspring Trade offs: offspring quantity vs. quality within a brood current vs. future offspring From the point of view of the parent Clownfish don t have opportunities to desert Tradeoffs shown in gobies, lizards, burying beetles, flycatchers p.228 Flexible care influence of costs and benefits Male vs female care influenced by chance of future RS, amount of brooding benefits Who cares? Another factor that determines if you care is what your mate does. P = offspring survival prob. p = probability to mate again W = # young, fem. deserts w = # young, fem. cares In fish, W often >> w, so if P 1 >>P 0 you will get care In birds P 2 often >>P 1 1

2 Mate conflict over biparental care What if a mate cheats by offering reduced care? Mate should compensate, but not fully Model both supported and refuted How much should parents care? Parent - offspring conflict Parents and offspring share 50% genes Conflict occurs over parent s allocation 1) within a brood and 2) towards current vs. future offspring Parent offspring conflict over length of parental care POC predicted in a model by Robert Trivers Assessing value Parents may allocate according to the value of their young. Offspring try to manipulate parents for more care. Look for honest signals of health 2

3 Intra- and interbrood conflict Intra- and interbrood conflict fur seal lactation conflict Booby siblicide Siblicide and parental manipulation Function of hatching asynchrony Parents may naturally invest more in some young and less in others. Ex: hatching asynchrony Bias in care can lead to siblicide Sibling eviction 3

4 Siblicide in birds Kookaburras 3 eggs in a clutch, but half the time not all will survive due to resources. Chicks try to kill each other Cattle egrets Female lays 3 or more eggs but only rarely will all survive 1 st egg is provisioned with testosterone Basic types of mating systems Mating systems Monogamy Polygamy Polygyny Polyandry Polygynandry (Promiscuiity) Mating systems: no paternal (male) care Generally, different forms of polygyny So..will the females clump? The form of polygyny depends on how females are dispersed around, influenced by: Scramble competition polygyny Lek/chorus polygyny Constrained monogamy Resource defense polygyny Harem defense polygyny (can be seasonal only) 4

5 Timing can be everything Operational sex ratio and synchrony of female availability, no male care horseshoe crabs Explosive synchronous breeding can limit multiple mates for males Mating systems: (no male care) Females solitary, unpredictable, synchronous breeding. Males selected for persistence and speed. Scramble competition polygyny milkweed leaf beetle two male butterflies wait for a female to emerge from cocoon 13-lined ground squirrel Mating systems: (no male care) Majority of mammal species: females solitary, males overlap their range w/several females Facultative polygyny Female ranges Mating systems: (no male care) Females social, their RS depends on resource that males can defend Resource defense polygyny Breeding habitat Male ranges Languar males owns harem in his territory long-horned beetle males defend foraging areas hoary marmot males defend feeding areas - food is scarce 5

6 Mating systems: (no male care) Females social but roaming or seasonal Harem/female defense polygyny Mating systems: (no male care) Polygynandry: when both genders have multiple mates. Females are usually in groups Multiple males defend group (lions) Groups meet up temporarily with male groups (dolphins, elephants) Mating systems: (no male care) Leks or chorus (Lek polygyny) Males clump - No resource or harem defense, females often have large ranges Female choice is extreme - center male gets most of the matings groups of 100+ males Success for males on leks sandpipers fallow deer lesser short-tailed bat 6

7 Why do males join these leks? Hotshot hypothesis Stimulus pooling Hotspot hypothesis Female choice hypothesis Hotspot: Males follow pattern of female dispersal Leks can occur at same spot year after year Stimulus pooling: More females are attracted to a set of males than separate male increased signaling Rewards to males increase with lek size Hotshot: Poor signalers parasitize the attention gained by highly attractive males Some manipulations don t support great snipe fallow deer 7

8 Mating systems with male care Female choice: Leks form because they allow females to make the best choice. Females choose vigorous males Females ignore males that aren t in leks How to increase RS when resources cause home ranges to overlap w/just 1? Obligate monogamy (p.257) Breeding habitat Mating systems with male care Obligate monogamy with biparental care Removal of a mate results in large RS failures Mating systems with male care Polygynandry with male care ostriches Dominant males and females form bonds, but also mate w others. Communal nests are formed with eggs of multiple females. Both care. Eggs of dominant female are in center (other females leave to form other nests) 8

9 Mating systems with male care Why be serially monogamous? French angelfish gibbon swans Mating systems with male care Monogamous, but by constraint Male removal decreases RS, but not enough to explain monogamy If RS to 1/x, male needs more than x females to be profitable (or care) beaver Mating systems with male care Polygyny occurs, but is rare in birds ~8%) Females can suffer from sharing benefits, males control needed resources Polygyny threshold model: similar to IFD model, females make choices regarding territory quality and monogamy vs. polygyny 9

10 Mating systems with male care Polyandry (sequential or resource defense) Possibly increases RS when clutch size is limited Jacana Phalarope Human mating strategies No animal illustrates behavioral flexibility as deeply as humans Culture determines much of human behavior can have female infanticide Human mating strategies Providing biological reasons for human behavior can be controversial: Implies the behavior is innate and immutable Humans debased, on the level of other animals Findings can be misused Cultural universals Persistence and recognition of bond (monogamous or polygamous) EO Wilson founder of sociobiology 10

11 Cultural universals Big paternal investment Long dependency period (language, tools..) Why female care alone is not enough Male lactation? Cultural universals Reassurance of paternity Males traditionally control wealth Penalties for adultery in women chastity belt Humans are odd, sexually Long-term pairing with paternal care Ovulation is concealed sex occurs often and irrespective of fertility Both sexes are choosy (not that unusual w animals w pair bonds) Some enhanced sexual signals compared to apes (breast and penis size) Why the mystery?? Human mating irrespective of estrous Estrous hidden, mating during pregnancy and after menopause Sex is fun and promotes bonding does not explain perineal swellings is this woman ovulating? 11

12 Why the mystery?? Paternity hypothesis (Alexander and Noonan) mate guarding, neighbor fertilities uncertain. Female receptivity promotes monogamy Infanticide hypothesis (Hrdy) confusion of paternity in face of infanticide. Female receptivity promotes polygyny Why the mystery?? Monogamous primates are almost always concealed ovulators However primates w/concealed o. may be monogamous or highly polygamous (harems) Human mate choice Similar to other animals with biparental care, both sexes participate in choice, using mutual fitness indicators Sexual strategies hypotheses Males and females look for different qualities b/c they have different reproductive challenges Male preferences Female preferences Short term sexually accessible quick resources low investment good genes inc.# partners Long term paternity certainty investment parenting ability parenting ability good genes good genes 12

13 Male preferences Males look for youthfulness and child bearing/rearing capabilities Breast size estrogen effects.7 waist to hip ratio Female preferences Females try to balance their preference for high T effects (better provider, defender) with low T effects (better parental care) (T is thought to be harder to maintain due to immunosuppressive effects) Preferences of males and females may alter with menstrual cycle Women s preference for men vs. cycle Men s preference for women vs. cycle 100 Responses to 3 questions for males and females % yes Q1 Q2 Q3 Women s preference for long-term relationships for pill users vs. non 13

14 Menopause is odd, too Menopause is found only in humans and some whales (pilot, orca) Why is there NS for the halting of reproduction? (and only in females?) Older women take on more risk for less potential gain when reproductive H&G tribe: Post reproductive women gather the most food of all Orcas have higher RS when grandmothers present in group 14