Ornithology Exam 3

Sexual Selection

The difference in mating or fertilization success that arises from contests among males for mates and female preference for specific males

Sexual Selection Reality

Preferences in one sex drives the evolution of appearance & behavior in the opposite sex

What does sexual selection explain?

the existence of characteristics that do not confer a survival benefit, heritable

3 Hypotheses for Sexual Selection

- good genes

- direct benefits

- arbitrary choice & runaway selection

Good Genes Hypothesis

Elaborate plumages/displays signals genetic/physiological quality

Handicap Hypothesis

a male that can support a costly and unwieldy ornament is likely to be a vigorous individual whose overall genetic quality is high

Direct Benefits Hypothesis

female prefers male that provides tangible resources that increase fecundity; not necessarily genetic benefits

Arbitrary Choice & Runaway Selection Hypothesis

Sexual selection evolves through arbitrary choice and runaway selection for aesthetically pleasing features with no evolutionary advantage (can be heritable)

Results of Sexual Selection

sexual dimorphism

Why is sexual selection usually shown in males?

the sex that has the lower reproductive burden is the one in which sexual selection primarily acts

Pharalopes

females show sexual selection driven traits and lay many clutches, leaving males to incubate and care for young

Types of Displaying

- Courtship Building

- Vocalizations

- Lekking

Courtship Building

ex: male baya weavers build nests that females judge, selecting the male with the best quality nest

vocalizations

calls and songs themselves are often displays that have been selected for over time via sexual selection

lekking

The gathering of males in an area for the purpose of displaying to attract females. (no resources aside from being a place to display)

3 Hypotheses Behind Lekking

- Hot Spot Model

- Hotshot Model

- Female Preference Model

Hot Spot Model

males gather at sites where they are most likely to encounter roaming females; good positioning offsets the cost of competition

Hotshot Model

males gather around experienced, attractive, or dominant individuals to increase their chances of being noticed

female preference model

- females prefer to visit large clusters of males over small clusters or solitary males

- allows females to make safer and more efficient comparisons between individuals

kin selection in lekking

birds can benefit via increasing the fecundity of genetic relatives, even at the expense of their own reproductive success

Ruff Lekking

3 types of makes:

- independents (display at leks)

- satellites (track wandering females and are recruited as display partners)

- faeders (look like females and solicit copulations)

sex determination in birds

all birds have 2 sexes; determined at fertilization

female ability to control sex ratio

female birds can bias the sex ratio of their offspring based on their physical condition or needs of parents (unknown how)

Bilateral Gynandromorphy

Create offspring with half body of a female and half of a male

What are the 4 sexes of white-throated sparrows?

- white striped (male or female)

- tan-striped (male or female)

white-striped white-throated sparrow

aggressive, tuneful, poor parent, mates with tan-striped

tan-striped white-throated sparrow

less aggressive, better parent, mates with white-striped

Bird Sex Hormones

testosterone (aggression & courtship) and estrogen (parent care)

bird testes are internal

- attached to the dorsal body wall of the back of the kidney

- sperm evolved to survive high temps

do birds have penises?

ancestral trait, waterfowl and some other taxa have penises, but most do not

How do birds mate?

cloacal kiss

cloacal protuberance

sperm are stored at the terminal end of the vas deferens (seminal glomus), and this creates a swelling

how often are bird copulations?

rapid and frequent during egg laying; up to hundreds per clutch of eggs

bird sperm competition

- sperm from multiple males can internally compete to fertilize eggs

- females can eject sperm though generally most recent is most likely to fertlize

Male Adaptations for Sperm Competition

- larger testes, sperm stores, & frequent copulations

egg development

ovum -> yolk -> germ cell (20 hours)

how many ovaries do birds have?

1

Parthogenesis

birds cannot reproduce via unfertilized birth due to sex determination method

What is the purpose of eggs?

provide protection and containment for all of the nutrients necessary to build a hatchling from an avian embryo

What do eggs require?

external heat, periodic turning, and defense from predators and brood parasites

How is egg shape influenced?

stronger flight = more elliptical/asymmetrical eggs

Analogous to human placenta

chorioallantoic membrane (exchanges O2 and CO2)

Proximate effects on clutch size

- huge metabolic costs

- 20% energy transfer efficiency

Capital breeders effect on clutch size

stored resources are used to produce eggs

Income breeders effect on clutch size

- based on caloric intake

- need to acquire calcium

Ultimate factors that affect clutch size

- shaped by natural selection (varies from 1 to dozens)

- depends on ability to incubate eggs/care for fledglings

monogamy

predominant avian mating system (~90%) with 2 parents involved in the raising and care of offspring (typically when male help is essential)

serial monogamy

monogamous for a single breeding season or nesting attempt, typically practiced by songbirds (migration mortality)

lifelong monogamy

common in long-lived birds and occasionally short-lived species and resident birds

divorce

Some birds will leave their pair bond for higher-ranked/better-adapted individuals (infidelity is incredibly common)

Extra Pair copulations (EPC)

A mating by a male or female with someone other than their primary partner in a socially monogamous species, 76% of monogamous species (common in Passerines)

EPC Costs and Benefits

- both sexes willing

- both leave territories

- maximizes fitness

EPC Benefits in Females

- insurance against infertility

- more genetically diverse brood

- improved genetic quality

- increased access to resources

EPC Costs in Females

- reduced parental care

- increased risk of harassment from mates

- increased risk of STIs

EPC Benefits in Males

- insurance against infertility

- more offspring

- future mate acquisition

EPC Costs in Males

- sperm depletion

- increased risk of divorce/partner infidelity

- reduced parent care

- increased risk of STI

Polygyny

One male, several females, evolved in clumped resource territories

Polygyny Behaviors

- fruit/nectar diets favor polygyny

- heavily associated with lekking

3 Types of Polygyny

1. Female Defense Polygyny

2. Resource Defense Polygyny

3. Male Dominance

resource defense polygyny

males defend territories rich in resources that are used by and attract females

female defense polygyny

Polygynous males directly defend several females.

male dominance polygyny

a mating system in which a few males on a lek mate with many females

male trade-off hypothesis

Polygynous males are so preoccupied with other females they should experience greater levels of cuckoldry (lower paternity rates)

Female choice hypothesis

Females discriminate against solitary males

Comparing phenotypes by the female is easier in groups of males

polyandry

One female, several males (mostly charadriiformes and gruiformes)

hormonal changes in polyandry

sandpiper females have higher testosterone during mating

cooperative polyandry

several males defend a female's territory

brood parasitism

one egg-laying species benefits by having another raise its offspring, eggs develop faster and young fledge sooner

types of brood parasitism

- conspecific/intraspecific (same species)

- interspecific (different species)

conspecific brood parasitism

females facultatively dump their eggs in the nest of other females of their own species

why parasitize conspecifics?

- first step towards evolution of interspecific brood parasitism

- insurance in event female's primary nest is depredated

facultative interspecific brood parasitism

can build own nest, but sometimes dump eggs as well

obligate interspecific brood parasitism

- only way to reproduce; never build own nest (some cowbirds, some cuckoos)

Generalist Brood Parasite

parasitizes multiple different host species

- offspring may kill host eggs

- rejected parasites have nests destroyed

Specialist brood parasites

only parasitizes a single species

defense against brood parasites

- increased nest vigilance

- abandoned nests

cooperative breeding

helpers care for young that is not their own (for experience and inclusive fitness)

Gaining Experience

birds that serve as helpers first have higher lifetime reproductive success

kin selection

the idea that behaviors that help a genetic relative are favored by natural selection

reciprocal altruism

behavior that benefits another with the expectation that those benefits will be returned in the future

why cooperative breeding?

A behavioral pattern in which young birds postpone breeding and instead help their parents raise offspring (in limited locations)

animal architecture

constructions from a variety of natural materials utilizing specific methods to create highly functional designs

nest architecture goals

- protection from predation and parasites

- maintains an adequate microclimate

where do birds build nests?

isolated/hidden places

diversity of nest architecture

- cup

- dome

- dome & tube

- plate/bed

- scrape

- burrow

- mound

nesting materials

many different external materials, sometimes stolen, sometimes none at all

Nest Substrates

- woody vegetation

- grasses

- ground

- wall/ledge

- burrow

- tree cavity

- floating

- animal products

Cavity nesting

- primary (self made)

- secondary (uses other birds')

Weird nesting habits

- spiderwebs by hummingbirds

- hardened saliva by swiftlets

- tree branch by white terns

passerines

most diverse nests, pensile nests

Nesting is inherited

- considered an extended phenotype, but experience matters

evolutionary pressure

nest evolve from avoiding predation

Nest evolutionary history

- began as ground nesting

- diverse in neoaves; adaptive radiation

who builds the nest?

either member, typically both in monogamous species

site selection

important part of pair bonding/mating

nest safety

1. Invisibility

2. Inaccessibility

3. Impregnability

invisibility

- camouflaged eggs

- camouflaged nests

- cryptic locations

inaccessibility

- placed in areas difficult for parasites and predators to get to

impregnability

- physically impenetrable or confusing to enter

nest microclimates

impacted by placement and design