1

Burying beetles, clownfish

Rare ectotherm biparental care

Parent beetles bury, defend, shave, roll, ‘inoculate’ carcass

Clownfish don’t have opportunities to desert

Trade offs:

offspring quantity vs. quality within a brood

current vs. future offspring

Determining optimal parental investment per offspring

From the point ofview of the parent

Tradeoffs shown in gobies, lizards, burying beetles, flycatchers p.228

Male vs female care influenced by chance of future RS, amount of brooding benefits

Flexible care – influence of costs and benefits

Another factor that determines if you care is what your mate does.

Who cares?

P = offspring survival prob.p = probability to mate againW = # young, fem. desertsw = # young, fem. cares

In fish, W often >> w, so if P1>>P0 you will get care

In birds P2 often >>P1

2

What if a mate ‘cheats’ by offering reduced care?

Mate should compensate, but not fully

Model both supported and refuted

Mate conflict over biparental careParent - 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

How much should parents care?

POC predicted in a model by Robert Trivers

Parent offspring conflict over length of parental care

Parents may allocate according to the value of their young. Offspring try to manipulate parents for more care.

Look for honest signals of health

Assessing value

3

Intra- and interbrood conflict

fur seal lactation conflict

Intra- and interbrood conflict

Booby siblicide

Parents may naturally invest more in some young and less in others. Ex: hatching asynchrony

Bias in care can lead to siblicide

Siblicide and parental manipulation

Sibling eviction

Function of hatching asynchrony

4

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 – 1st egg is provisioned with testosterone

Siblicide in birds

Mating systems

Monogamy

Polygamy

Polygyny

Polyandry

Polygynandry (Promiscuiity)

Basic types of mating systems

Generally, different forms of polygyny

The form of polygyny depends on how females are dispersed around, influenced by:

Mating systems: no paternal (male) care

Scramble competition polygyny Resource defense polygyny

Lek/chorus polygyny Harem defense polygyny

(can be seasonal only)

Constrained monogamy

So..will the females clump?

5

Operational sex ratio and synchrony of female availability, no male care

Timing can be everything

horseshoe crabs

‘Explosive’ synchronous breeding can limit multiple mates for males

two male butterflies wait for afemale to emerge from cocoon

Females solitary, unpredictable, synchronous breeding. Males selected for persistence and speed. Scramble competition polygyny

milkweed leaf beetle

13-lined ground squirrel

Mating systems: (no male care)

Majority of mammal species: females solitary, males overlap their range w/several females

Facultative polygyny

Mating systems: (no male care)

Female ranges

Male ranges

Breeding

habitat

Females social, their RS depends on resource that males can defend

Resource defense polygyny

long-horned beetle malesdefend foraging areas

hoary marmot males defendfeeding areas - food is scarce

Languar males ownsharem in his territory

Mating systems: (no male care)

6

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

fallow deer

lesser short-tailed bat

sandpipers

Mating systems: (no male care)Success for males on leks

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

8

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.

Mating systems with male care

Eggs of dominant femaleare in center (other females leave to form other nests)

9

gibbon

beaver

swansFrench angelfish

Why be serially monogamous?

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)

Mating systems with male care

Polygyny occurs, but is rare in birds ~8%) Females can suffer from ‘sharing’ benefits, males control needed resources

Mating systems with male care Polygyny threshold model: similar to IFD model, females make choices regarding territory quality and monogamy vs. polygyny

10

Polyandry (sequential or resource defense)

Possibly increases RS when clutch size is limited

JacanaPhalarope

can have female infanticide

Mating systems with male careNo animal illustrates behavioral flexibility as deeply as humans

Culture determines much of human behavior

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

Human mating strategies

EO Wilson – founder of sociobiology

Persistence and recognition of bond (monogamous or polygamous)

Cultural universals

11

Big paternal investment

Long dependency period (language, tools..)

Why female care alone is not enough

Male lactation?

Cultural universalsReassurance of paternity

Males traditionally control wealth

Penalties for adultery in women

chastity belt

Cultural universals

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)

Humans are odd, sexuallyHuman mating irrespective of estrous

Estrous “hidden”, mating during pregnancy and after menopause

“Sex is fun” and “promotes bonding” does not explain

is this woman ovulating?

Why the mystery??

perineal swellings

12

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)

Why the mystery??

Human mate choiceSimilar 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 abilitygood genes good genes

13

Males look for youthfulness and child bearing/rearing capabilities

Breast size estrogen effects

.7 waist to hip ratio

Male preferences Female preferencesFemales 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

Men’s preference for women vs. cycle

Women’s preference for long-termrelationships for pill users vs. non

Women’s preference for men vs. cycle

Q1 Q2 Q3

100

75

50

25

0

% yes

Responses to 3 questions for males and females

14

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

Menopause is odd, too…