A) Consider general patterns of variance in parental care

Although investment in offspring can take many forms, care after egg laying, birth, or hatching typically referred to as parental care.

As with other aspects of animal behavior, general patterns of care can best be understood by considering parental behavior as an adaptive strategy that maximize individual reproductive success.

1) The need for care is linked to type of offspring.... this can be linked to organismal biology.

Basic patterns of care found within different vertebrate taxa:

 

 

 

Taxa specific examples of parental care

For ectotherms, care is generally not a requirement for offspring survival.

Fish: Care is mostly related to anti-predation strategies and is usually minimal

Swamp predators (large mating swarms)

Hide/stash eggs (salmon, grunion, needlefish)

Guarding eggs in a nest (blennies, damselfish, stickleback)

Male builds/defends substrate for laying

Protection (also fanning and cleaning in brackish water)

Mouthbrooding (cichlids, jawfish)

Guarding of eggs and mobile fry (cichlids, toadfish)

Viviparous (guppies, sharks, rockfish)

Amphibians like fish: most care is related to anti-predation strategies

Swamping (large egg masses in Rana and Bufo)

Hiding/stashing (eggs over water Phylomedusa; dispersal of eggs over large area, some Rana)

Guarding eggs in nest

Males (Glass frogs in the genus Centrolene)

Females (salamanders)

Carry eggs and/or young

Males carry (midwife toad on legs, dendrobatids on back, Rhinoderma in vocal sacs)

Females carry (imbedded on back: Stefania or within pouch: Gastrotheca and Flectonotus)

Internal fertilization (Nectrophyrnoides)

Reptiles (care is not common, except for egg burial/stashing)

Female guarding of eggs and/or young (cobras, crocodilians)

A few examples of incubation of eggs (skink, python) where muscle twitching creates heat

 

 

For endotherms (birds and mammals): small, warm-blooded animals have high metabolic demands that require food or protection. Thus, parental care, at least in terms of incubation or gestation/lactation are a requirement.

Birds (biparental care the norm)

Male help significantly increases brood success for most birds

Some good examples of various forms of parental care in birds

Mammals (female care the norm)

Males can help by:

Guarding

Feeding older young or provisioning the mother

Carrying offspring

 

Occurrence of different types of male vs. female parental care

Organism	Male only	Female only	Male & Female	Female viviparous	No parental care
Fish	50 families	6 families	10 families	22 families	180 families (79%)
Amphibians	11 families	11 families	0 families	3 families	>100 families
Reptiles		< 5 % of species			> 95% of species
Birds (altricial)	1 % of species	7 % of species	93 % of species
Birds (precocial)	8 % of species	17 % of species	75% of species
Mammals		~ 95% of species	~ 5 % of species

 

General trends from fish to mammals:

Total parental investment per offspring increases

Clutch size decreases

When parental care is expressed

The proportion of species with female care increases

The proportion of species with male care decreases

Parental care linked to mating system

Fish and amphibians: male care or no care/polygamy

Birds: biparental care/monogamy:

Mammals: female care/polygyny:

Remember, for each of these generalizations there are exceptions (e.g. ungulate mating systems)

 

2) Understanding why patterns of parental care exists across taxa (who gets stuck with what)

Potential for increased reproductive success from other matings may often select for males who desert females.

Birds are the exception: demands of parental care are generally too great

Male mammals, initially emancipated from the demands of parental care, are most likely to desert.

Fish show all patterns and are a good group for investigating parental care with relation to mode of fertilization:

External fertilization: 71 % male care

Internal fertilization: 86% female care

Explanations:

Confidence of paternity (lower with internal fert.... so males less likely to care)

Order of gamete release (who is stuck with the eggs last)

Association (care is a by product of adult biology)

Given the potential conflict between parents over who cares for offspring, an ESS approach is appropriate for examining the "decision" to care or not to care.

 

B) Now consider the consequences of limiting parental care from two perspectives:

Variable parental care and parent/offspring conflicst

In some parental care systems, males or females provide care, but it is limited in extent below what an individual offspring would prefer

Some examples

Nonuniform care of brood:

Larger vs smaller (seabirds)

Male vs female (blackbirds)

At an extreme, young are killed by their parents

Filial cannibalism (consumption of all or part of a current brood)

If adaptive, then the presumed costs of brood loss should be compensated for by increased survival of the cannibal and greater future reproductive output

Such behavior is most common in male fish with parental care (damselfish, gobies, sand darters... also some broadcast spawners, e.g. razorfish)

partial clutch

whole clutch

Can be understood in terms of investment towards either:

future broods (expect increase in cannibalism with decreasing brood size)

current brood (expect partial cannibalism to increase with increasing brood size)

In either case, expect decreased cannibalism with increasing age of brood.

Infanticide (killing without consumption) can be selected for if it increases the likelihood of future reproduction vs sticking with the current brood.

females making the best of a bad situation

males with low confidence of paternity

Strategies for consumption of offspring may be limited by parasites?

There is an increased opportunity for parental conflicts when the products of different broods overlap in time (parents are given the opportunity to partition care among offspring of different age or life history stage)

Offspring don't disperse

Generation time is short

Both of these conditions may lead to opportunities for despotism or cooperation within a family.

Total freedom from parental care: Lek mating systems (pg 254 - 264 in text)

Defining "Lek" Behavior

The classical definition of lek mating behaviors include:

1. No male parental care.

2. Males aggregate at sites within total home range, display communally, and females visit these sites to mate.

3. Display sites (called "leks") contain no essential resources females need.

4. Females have choice of mate at display aggregations.

Examples are found in a diverse assemblage of organisms: e.g., sage grouse, manakins, Uganda kob, hammer-headed bats, widow birds, Hawaiian Drosophila.

Questions to consider with regard to leks:

Why/How do leks evolve?

Explanations for classical lek evolution:

1. Males are emancipated from parental care by

Diet

Predator risks

Precocial young.

2. Neither resource nor female defense energetically feasible.

3. These are not mutually exclusive

Look at general patterns of lekking for hints as to how they evolve

First off, there is variance.

Some mating systems resemble leks, but only partially fulfill the definition of a classic "lek":

1. Many species have no parental care, no defended resources, and females can choose mates, but males are only slightly clustered (exploded leks) or not clustered at all. Examples: birds-of-paradise, bowerbirds, bellbirds, epauletted bats, blue grouse.

2. Some species have no parental care, males are aggregated, and females can choose, but resources play some role in male dispersion and perhaps female choice. Examples: frogs, long-tailed whydahs, dragonflies.

3. Many insects have no parental care, males form dense aggregations which females visit for mating, there are no resources involved, but females do not have a choice of mate. Bees, caddisflies, mayflies, various true flies.

What does this tell us?

Imposing strict categorical definitions can obscure the fact that several independent options must be brought together to produce a classical lek.

It is not necessary that these same options must always occur together. Hence one can get the lek-like systems.

Instead of relying on such categories, better to accept that different combinations of options will occur from the start and use different mixes to understand how each option is favored or not favored.

Why do females choose particular males for mating?

Female Choice of Mates on Leks

A. Leks are THE place to study dynamics of female choice sexual selection.

B. Two approaches to studies of female choice:

Correlative studies (matching measures of various trait values and mating success)

Experimental studies (manipulating male traits to see whether this affects mating success.

Both have clearly indicated that elaborated male traits are being used by females to choose mates. Traits include:

Plumage patterns in some lek birds (birds of paradise)

Display performance (sage grouse, great snipe, Jackson's weavers, Lawe's Parotia, fallow deer)

Bower decorations (bower birds).

Male traits don't explain everything.

Even in best studies, male traits account for only a moderate fraction of overall variation in male mating success.

Three hypotheses regarding other sources of variation

Position Effects: If mate choice is difficult or costly, females may simply return to previously used sites instead of recomparing all males.

Copying: If mate choice is difficult or costly, females may copy other females instead of assessing males themselves.

Male Interference: On smaller leks, a few males may be able to interrupt and/or dominate the remainder of males and thus obtain all the matings regardless of female choice.

C. Costs of Sexual Selection on Leks

Sexual selection creates different relationships between use of resources and offspring for males and females

Males should be risk prone and females risk averse.

Cues which are important to females should be associated with mortality in males.

So, in leks, parental care by males is obviously limited (i.e. it's not expressed)

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