Mating Systems and Parental Care

Comparative ApproachCost-benefit ApproachMechanism Approach

Monogamy – one male and one femalePolygyny – one male, multiple femalesPolyandry – multiple males, one female Promiscuity – multiple, multiple

} Polygamy

Mating Systems and Parental Care

Birds both male and female MonogamousMammals female only PolygynousFish male only Polygamy/promiscuity

In birds, polygyny often occurs in fruit and seed eaters because these foods can become so abundant that one parent can often care for the young alone...

and it is the male who deserts first...why?

-- With internal fertilization, the male often has the first opportunity

-- With internal fertilization, certainty of paternity is never guaranteed

-- The male has more reproductive success to gain – greater selection pressure

Male 2 61Female 14 24Neither 5 100

internal externalPar. care

Male parental care is commonest with external fertilization, Female parental care with internal fertilization

(1) Paternity certainty – still uncertain

(2) Order of gamete release – N/A

(3) Association – internal fertilization leads to greater female association whereas in fishes, eggs are laid in male’s territory and he is most closely associated with the embryos – territoriality to attract females becomes coupled with nest and offspring defense

Families of Teleost fishes

P0,1,2 = probability eggs survive given 0, 1, or 2 parentsW, w = eggs laid by deserting or caring female, respectivelyp = probability deserting male mates again

Care

Desert

F: wP2 WP1

M: wP2 WP1

F: wP1 WP0

M: wP1 (1+p) WP0 (1+p)

Care Desert

FEMALE

MALE

If female cares then male should desert if: wP2 < wP1(1+p)

Cost/benefit approach

Care

Desert

F: wP2 WP1

M: wP2 WP1

F: wP1 WP0

M: wP1 (1+p) WP0 (1+p)

Care Desert

FEMALE

MALE

- caring/deserting by parents is a game between 2 players: M & F

- the best decision by one player depends on the decision of the other

- we can understand caring/deserting in terms of the probability of remating (M), eggs laid (F) or loss of offspring when raised by a single parent (M and F)

- Environmental conditions that abruptly alter these costs and benefits may also abruptly alter parental care and mating strategy – e.g., facultative polygamy

Birds

Social Monogamy - 90% of all birds

Factors that promote monogamy and biparental cases are oviparity and endothermy b/c 2 parents often required for successful reproduction

Pair bonds may last for life (e.g., parrots, albatrosses, eagles, geese, pigeons), but separation is quite common, and usually after failed breeding attempts.

Mute Swans: 5% of breeding pairs and 10% of non-breeding pairs separate each year

What do males do?

Are males necessary?

(1) Shared incubationWestern sandpipers – removal of either parent led to

100% failure

(2) Female provisioning – common in raptors, hornbills, and other groups

7 of 8 male kestrel removals resulted in nest abandonment (the exception wasa female who lost her mate on day 24 of a 27 day incubation period)

(3) Post-hatching care - Effects of male-removal on nesting productivity…

Song sparrows – decrease by 51%Seaside sparrows – decrease by 66%Dark-eyed juncos – decrease by 38%

Also in kestrels, rock doves, tree swallows and other passerines.

(4) Post-fledging care – 3 passerine studies show loss of male leads to 37-66% reduction of young to independence

EPCs – Extra-pair copulations – copulations outside the pair-bond

- Once thought to be very rare … until DNA-fingerprinting become common, now it appears everyone is doing it.

offspring fathered by extra-pair matings

Black Vulture 0Common Loon 0Ea. Screech Owl 0Willow Warbler 0Fulmar 0 Wood Warbler 0Eu. Bee-eater 1Zebra Finch 2Pied Flycatcher 4Blue Tit 18Shag 18Red-winged Blackbird 28Purple Martin 35Indigo Bunting 35Superb fairy-wren 76

EPCs in the Red-winged blackbird

Benefits to EPCs

Males – sire more offspring so long as the xtra effort does not compromiseparental effort with its social mate

in value of paternal care

# opportunities (density of females)

in the ability to guard mate} Will the

prevalence of EPCs

Females – No gain in the # offspring, so why engage in EPCs?

(1) It is forced – Mallards (2) Insurance against infertile males(3) Sperm competition – may the best sperm win

or….

(4) Good Genes

Most females cannot mate with the best male (constraint) so they seek out EPCs to increase their overall fitness

Predicts: Females will seek EPCs with better males:

Test: Zebra finch (Houtman 1992)

0 +2 +4 +6-4 -2

Difference in rank between social mate and EPC-mate

ImprovementDown-grading

# males

Zebra finch

= EPCs

This begs the question of why not have more EPCs with the best/better males? …Probably risk of mate-abandonment if confidence of paternity is compromise

from EPCs to polygyny

Social/geneticmonogamy

Females mayseek EPC

Male parental care is not essential

Male response: Increased mating effort Decreased parental care

= Polygyny

(1) no other choice – best of a bad situation

In Picman’s (1987) study of the marsh wren females settle with mated males only afterall bachelor males had paired

Deception model posits that the female pays a cost of polygyny b/c the male conceals its bigamous relationship from the females

Male and femalePied Flycatchers

10-15% of males are successful at having 2 mates separated by 0.2 – 3.5 kmapart thereby concealing the 2 relationships from each other

Male Female #1

Some distance away

Deception model male conceals its bigamous relationship from the females

Female #2No male assistance

Females must decide whether to (i) mate with an already mated male on a high quality territory or (ii) an unmated male on a poor territory.

The threshold is the point at which a female will do as good or better with option i

abcde

#1

1 ♀

2 ♀

FemaleReproductive

success

Territory Quality

Polygyny threshold model posits that there is an uneven distribution of important resources that males control access to through territoriality

abcde abcde

#2

abcde

#3

abcde

#4#5

#6

In conclusion, there are 3 scenarios that may lead to Polygyny:

(1) Females have no other choice but to mate with a mated male

(2) Females may be deceived

(3) Males control access to resources, but also Females may actively assess the consequences of their decisions and make an adaptive choice

....let’s examine this relationship between resources and females more closely in mammals....