Mating Systems

Mating Systems (Includes 3 things)

includes all of the behaviors involved in acquiring a mate including the nature of the social bonds between the sexes (if there are any) and contribution of sexes to parental care

Basic behaviors that help define a mating system: (6)

• display behaviors

• intersexual competition for males

• sexual division of investment in gametes or parental care

• copulations (frequency, timing, and with whom)

• social pair bonds

• whether or not juveniles help

Factors Used to Categorize Mating Systems: (3)

• social pair bonds

• gene flow

• ecological factors

How mating systems are described

• most birds have one dominant behavior used to describe their mating system

  • within a main mating system, some or even most individuals of a given species may use alternative or opportunistic tactics (ex. extra pair copulations)

2 Broad Categories of Mating Systems:

1. Monogamy

2. Polygamy

Monogamy in Birds (stat & specific term)

• 90% of birds are monogamous

• specifically they are socially monogamous

Socially Monogamous

help each other to raise their kids but take advantage of other copulations when they can

Monogamous Systems (what does this mean? how is it inferred?)

each male and female have a full on social bond with one other individual

• this can be inferred from close proximity and coordination of breeding activity

Monogamy in Fishes & Mammals (how prevalent & why)

only around 3% are monogamous

• because there is less parental investment

  • males cant provide incubation or milk

Example of a Mammal that IS Monogamous

Wolves

• males can provide food

Polygamy in Birds (stat + what it is)

• 10% of all bird species are polygamous

• males or females pair with one or more individual

Types of Polygamy: (4)

1. Polygyny

2. Polyandry

3. Promiscuity

4. Variable Systems

Polygyny

1 male with 2+ females

Polyandry

1 female with 2+ males

Promiscuity (what? does this imply the same things as for humans?)

usually no male care provided at all

• does NOT imply indiscriminate mating

Variable Systems

can vary depending on level of competition surrounding pair bonding

What explains the unusual presence of monogamy in birds? (3 things)

1. Endothermy

2. Males can help

3. Lack of opportunity for polygamy

Endothermy

• they have fragile eggs that require many days of incubation

• males can contribute either through provisioning the female or by sharing in the duties of incubation

How can male birds help compared to mammals?

• males have the ability to provide valuable parental care after the chicks have hatched (provisioning chicks)

• most mammals and fish cannot help in this regard

Lack of opportunity for polygamy (3 reasons)

• highly synchronous breeding

• high levels of competition

• resources aren’t clumped

Example of a lack of opportunity for polygamy

Longspurs

• mate over only 1-2 days

Conditions under which polygamy can evolve: (2)

• mates/resources have to be defendable

  • most likely spatially or temporally clustered (so one male can take control of the resources)

• individuals have to be able to take advantage of those potential opportunities

Why is polygyny generally more common than polyandry? (3 reasons)

• females have to invest heavily in eggs

• males are able to desert as soon as copulation occurs- sperm is cheap!

• tends to be a lack of certainty of paternity

Costs and Benefits of Mating Systems

• each system might have different costs & benefits for mates, which might lead to competition among individuals for control of that particular bout of mating

Pied Flycatcher (what kind of bond?)

a male and female form a primary care bond

Cost & Benefits- Male Pied Flycatcher

when the female mates with the territorial male and starts setting up her nest, that male will move to a distant secondary territory in an attempt to find a second mate (so the first female doesn’t find out)

• secondary females are tricked into thinking they are the primary mate, but they usually have lower reproductive success because the male puts most care into the primary female

• no cost, high benefit

Cost & Benefits- Female Pied Flycatcher

females which lose their mate during incubation actively solicit copulations from neighboring males

• they want to trick them into helping raise offspring that aren’t theirs

• only happens during incubation

Salt Marsh Sparrows Study

no territorial defense, no parental care, no pair bonds

• males and females only come together to exchange gametes

this system lends itself to multiple mating’s across species

Salt Marsh Sparrows Stats (3)

• in 57/60 broods- at least 2 of the chicks sampled and genotyped resulted from multiple mating’s by females

• ~1/3 of broods had a different father for each chick

• just over ½ of the nests had multiple fathers having fathered at least 2 or more chicks

Salt Marsh Sparrows- Distance of Male Nests

many males sire chicks in multiple nests up to 1.4km away from their original capture site

• some nests were up to 0.5km away from each other

• implies that they move around a lot to find these opportunities to gain fitness

Monogamous Systems Variation:

found within the length of the pair bonds

• can range from a couple of days to a lifetime (ex. swans, albatross)

Polygynous System Variation (2 Varieties)

1. resource defense polygyny

2. female defense polygyny

Resource Defense Polygyny (+ example)

linked to food or nest sites

• Red-winged Blackbird females tend to cluster together on better nesting territories

Polygyny Threshold Model

predicts that if male territories vary enough in quality, then a female settling on an already occupied but superior territory (as a secondary female) could rear as many offspring as she could by being a monogamous (primary) female on a crappy territory

• females must decide if they want to be the primary or secondary female

• this is true even if by settling on a better territory she has to forego parental assistance from the male

Polygyny Threshold Model- Label

X- Environmental Quality

Y- Female Fitness

A- Polygyny Threshold

B- Primary Female (1*)

C- Secondary Female (2*)

Polygyny Threshold Model Explained

the first female in the system will settle in the best spot (1) and they will line up after that going down the line (blue), with spots lowering in quality

• above the line = better fitness

• below the line = equal fitness

potential secondary female is gaining environmental quality by being a secondary female on a better territory, rather than being the sole female on a bad territory

Another Visual for Polygyny Threshold Model

Red-winged Blackbird territories are on the edge of a lake in cattails

• the farther from the water = worse territory

Female Defense Polygyny (precondition?)

males are defending groups of females rather than resources

• really rare in birds!

Precondition: natural clumping of females for some reason

Female Defense Polygyny Example

Oropendolas

• females like to nest together in trees for some reason

• males can potentially defend trees with all the nests in it

How to tell if a system is polygynous?

males are bigger than females

Polyandry (2 types)

1. Cooperative Polyandry

2. Sequential Polyandry

Cooperative Polyandry

2+ males mating with a female and assisting in rearing young

Characteristics of Cooperative Polyandry: (3)

• saturated environment

• very stable groups

• skewed sex ratio - more males than females

Cooperative Polyandry Example

Galapagos Hawks

• Galapagos Islands = not a lot of habitat available (saturated)

• Females hold maternally inherited territories (stable groups)

• very few females (skewed sex ratio)

Sequential Polyandry

females are mating with and laying clutches of eggs for a sequence of males

• males are the ones that have nests

• females are larger and are the territorially aggressive sex

Rare!!

Sequential Polyandry Example (Birds & Mammals)

Birds: Jacanas

• females will kill a male’s offspring in an effort to then lay eggs in his nest

Mammals: Lions

Normal Sex Ratio

50/50

Promiscuity

males and females only come together to mate

2 Types of Promiscuity

• resource defense

• display site defense

Resource Defense Promiscuity

males are defending a resource that females need to visit

• females leave after they use the resource and perhaps copulate with the male

Resource Defense Promiscuity Example

Orange-rumped Honeyguide

• resource being defended - honey

Why Display Site Defense? (2 reasons)

Display sites are set up if resources or females aren’t monopolizable

• either super abundant or difficult to defend

Precocial young render parental care to little to no value

• male doesn’t need to be there

Example of a Display Site (+2 bird examples)

a lek

• Manakins

• Grouse species

Display Sites - Manakins

lekking territory (area for elaborate displays/dances

Display Sites - Grouse Species

males come together and females pass through the territory

• best males (alpha) are in the middle, beta males are on the edges (but are important too)

• females still walk around and make choices!

Consequence of a lekking system

considerable variation in male copulation

(some get a lot, others get few, some get none)

Why should a lek even form? (2 reasons)

• potential hotspot

• potential hotshot

Potential Hotspot

females congregating in certain areas for some reason

Potential Hotshot

some younger, less successful males will cluster around the better males and learn from them

Variable Mating system Example

Dunnock

• depending on the environment, can show monogamy, polygyny, polyandry, or even polygynandry (multiple individuals of each sex)

Underlying Structure to Switching Between Mating Systems:

Sexes establish independently but generally have overlapping territories in relation to prey abundance

• when food is dense, male might overlap with one or more females

• at low densities, males can’t hold large territories and leave females with comparatively larger territories- female overlaps with multiple males

Driven by environmental resources and whose territories are overlapping

Extra Pair Copulations

Copulations that occur with an individual other than their social mate

• most individuals will take advantage of this if they can

  • very common (every avian family)

Most males participate because SPERM IS CHEAP!

How to Detect Extra Pair Copulations: (3 ways)

• genetic paternity testing

• plumage variation

• studies where the male of a pair bond has been vasectomized

Extra Pair Copulations Example

Purple Martins (take this to another level)

• colonial nesters

• older males arrive first on breeding grounds & establish a nest with a mate

• these males sing a special song to attract younger males later, once they establish a nest the older male mates with the mate of the younger males (cuckholded)

Purple Martin Fitness Results

Older males with their female have about 4.5 eggs

• by mating with the younger males females they add 3.6 eggs (increase in fitness)

Younger males are producing 30% of the eggs with their females (losing fitness)