L3- Parental Care

• African jacana→ male provides most of the care, protective brooding

  

Parental care:

• is a diverse trait

• varies within species in:

  • the form it takes

  • level and duration

  • extent provided by each/both parents

• encompasses a huge range of behaviours e.g.

  

Example of parental care→ mouth brooding:

• seen in many fish species

• e.g. female cichlids- mouth brood for 3-6 weeks, wont feed themselves→ cost of care but benefit to offspring

Parental care varies massively across species:

• provisioning of care occurs in 1% of insect species

• parents protect from predators→ cleaning, carrying, warming offspring

• some form of parental care occurs in 30% of fish families, amphibians (6-15% in anurans, 20% of salamanders) and reptiles (all crocodiles, 1% of lizards, 3% of snakes)

• less common in ectotherms→ most parental care occurs before they are born (e.g. egg guarding) but postnatal care can occur (e.g. mouth brooding)

Parental care in Insects-

• estimated ancestral states of parental care across different groups of insects:

  • phylogeny at the top of Holometabola→

    • have a mixture of female, biparental and no care

    • have no male only care

    • the fact that they have larval, pupal and adult stages may influence types of care

  • phylogeny of Hemimetabola→

    • have wider ranges of parental care including male only care

    • may be because there is no pupil stage

  

Parental care in Salamanders-

• there are only limited cases of male only care and is constrained to species with external fertilisation (light blue)

  

  → suggests male care can only evolve in species with external fertilisation

• females are less tied to offspring reproduction→ easier to desert or look for other mating opportunities

• there are examples of female only care→ some groups is almost ubiquitous

→ shows importance in modes of fertilisation and offspring development

• offspring development has many different forms in salamanders:

  • aquatic eggs- aquatic larvae

  • terrestrial eggs- aquatic larvae

  • terrestrial eggs- direct development

→ could be important in determining outcomes of paternal care

Parental care is not fixed at the level of species:

• there can be more than one mode of parental care in a population, within species→ e.g. 3 closely related species of plover:

  • White-fronted, Madagascar, Kittliz’s Plovers→ all same genus, co-occur on salt flats in Madagascar, share same environment

  • White-fronted and Madagascar have biparental care during incubation and brooding whilst Kittlitz’s has uniparental and biparental care

  • Q→ why are these closely related species that share the same habitats responding differently in terms of parental care strategies?

    → answer is in papers to be discussed

• some species show more than one mode in a population e.g. burying beetles, acorn woodpeckers, Galilee St. Peter’s fish and gray wolf

Why we see these differences in parental care form can be summarised into these series of questions:

• What are the principal benefits of parental care?

• Why does the extent of parental care vary so widely between species?

• Why do only females care for eggs or young in some animals, only males others, and both parents in a few?

• To what extent is parental care adjusted to variation in its benefits to offspring and its costs to parents?

• How do parents divide their expenditure between their sons and daughters?

Extent of parenting-

• broad idea that the extent of parenting is defined in terms of growth and survival of offspring, depends on the offspring themselves, has trade-offs

• demands of the offspring are very important e.g. skimmer provisioning its young with fish caught, nest is just a scraping of sand

  

• links to the precocial-altricial spectrum:

  • mostly seen in birds, quite a bit in mammals, looking at wider taxa now

  • is based on appearance and behaviour

  • idea was first proposed by Margret Morse Nice→ developed a classification scheme based on observations of different developmental behavioural characteristics of different species (Rick Clefs uses a similar scheme)

  • precocial→ born with downy feathers, hatch with eyes open, are mobile, able to feed themselves within a few hours of hatching, mostly ground nesting e.g. Wood Duck

  • semi-precocial→ more development, seabird species- cant immediately go out and catch fish e.g. Brown Nuddy

  • altricial→ born with no/few downy feathers (naked), hatch with eyes closed, nest bound, entirely reliant on parents food, parents regularly attend nest/are near offspring e.g. American Robin

    

  • super precocial→ abandoned by parents as soon as eggs are laid e.g. Australian brush-turkey:

    • nest is a mound of rotting compost that generates heat, lay 20 eggs, cover with sand for insulation, creates a steady environment for eggs to develop in, parents leave them

      

  • see varieties of developmental modes within closely related species e.g. phylogeny of shorebirds

    

  • precocial-altricial spectrum is important for evolution of parental care in these species:

    • morphology is similar across species in terms of thermal regulatory abilities but there are differences in if they can feed

    • whether they can forage constrain potential opportunities of mating for parents

    • evolutionary transitions from biparental care to uniparental care→

      • contingent on the prior evolution of precociality→ only see uniparental care if that lineage has already evolved towards precociality

      • no species in this had biparental care

        

    → suggests uniparental care is much more likely to evolve when demands of offspring are reduced

Forms of reproductive modes-

• oviparity- parent lays eggs

• viviparity- parent gives birth to live young

• varies but is more conserved in terms of major groups:

  • most mammals are viviparous

  • most fish and amphibians are oviparous

  • reptiles have a mixture

    

    • squamates have had >100 transitions across species of switches between o and v

      

    • controversy of direction of change but is harder to switch back to a development of an egg

    • discussions will look at transitions between these states and the constraints there are

    • if only evolution from oviparous to viviparous is possible, why do we still see oviparous at all?

      • something is happening at the macroevolutionary level

      • may oviparous have higher speciation rates on reproductive mode, which maintains oviparous species

• oviparity and viviparity are constrained evolutionarily→ don’t change across tree of life generally

• there are examples within reptiles of variation within species e.g. 3 species that vary in reproductive mode:

  • oviparous, viviparous, viviparous with transitional form of pregnancy

    

• reproductive mode varies spatially:

  • mapped where there are high proportions of viviparous squamates→ SA, central/north america, east coast of Australia east coast

  • mapped where there are high proportions viviparous squamates out of the whole species→ SA is now low, more northern, temperate, boreal, edge of tundras

    

  → potentially environmental/climactic drivers for the evolution of this

• reproductive mode links closely to sociality e.g. viviparous reptiles are more likely to display sociality (live in groups)

  

Constraint and opportunity:

• demands of the offspring can constrain the form, duration and length of care→ lower offspring demands provide opportunity for a wide range of modes of care

• if both parents are not required to ensure survival one (or both) can abandon the brood→ doesn’t mean they will though

• adults avoid cost of care through desertion→ could be beneficial for adult survival (reduced energy costs) or for seeking further mating opportunities

Sex biased survival-

• suggests where costs and benefits are when providing care

• sexual selection theory predicts higher cost of reproduction for the sex with more intense intrasexual competition

• parental care theory predicts higher mortality for the care-giving sex

• study looking at 194 cases where females have significantly higher annual mortality than males

  • method→ assessed the degree of mating competition- polyandrous (females desert and compete) vs polygamous (males desert and compete)

  • results→

    • High mortality in males when male-male competition is stronger (supports sexual selection hypothesis)

    • mortality is more male biased in more polygamous species

      

      → supports the sexual selection hypothesis

  • method→ looked at post-hatching parental care

  • results→

    • male mortality cost increases as they provide parental care

    • don’t see the same in females

      

  → females already have a high cost of reproduction in producing and laying/carrying the egg (higher mortality than males), and so the effects of care on mortality are only detectable in males

  → is seen overall on average, regardless of mode of care

Oher than direct costs of parental care, how could sex-biased mortality influence the decisions of females and males of whether to provide care?

• direct costs of parental care

• mating opportunities/social environment e.g. snowy plovers:

  • 6 year study in California of breeding demography

  • observed that females deserted 6 days after hatching and males attended for 29-47 days post-hatching

  • after desertion, 22 /60 females renested with new mates and 10/18 males that deserted early remated

• why are females more likelt to desert?

  • Males outnumber females ~1.4 : 1→ imbalance in population, more likely to find unmated male

→ social environment need to be studied over multiple field seasons but are important in determining whether individuals will desert

• has a follow up study: Does demographic bias in sex ratios generate different opportunities for mating for males and females and therefore shift the balance between the costs of care and benefits of desertion?

4 discussions→

• Parental care and the social environment→ how social environment can be an important determinant of parental care

• Consequences of parental care→ how parental care can determine variation in other traits, macro evolutionary consequences, broader scale

• Avian chick development and the altricial-precocial spectrum

• The macroevolution and macroecology of reproductive mode→ how and why do reproductive mode vary across the tree of life and drivers of this?