Sex and behaviour

Parental investment In this section we are learning about the parental investment in reproduction and its costs and benefits to organisms and their evolution

Production of gametes Sperm many produced with small energy store Eggs far fewer produced much greater energy store depends on species eggs will carry enough energy to allow young to develop, this limits development Eggs are a greater investment of resources by female compared to male sperm

Sessile organisms and sex Sessile animals are usually permanently attached to a solid substrate of some kind, such as a part of a plant, a dead tree trunk, or a rock Many sessile animals, including sponges, corals and hydra, are capable of asexual reproduction in situ  by the process of budding. Sex cells often released into water to enable movement and meeting.

Sessile organisms and sex Plants on the whole can be thought of as sessile. They produce gametes such as ova and pollen. They rely on distributive mechanisms to move the pollen such as water, air, insects, birds, bats and small mammals. The reproductive organs will be related to the form of gametes produced i.e. wind or insect pollinated flowers are very different.

Sexual reproduction Happens 2 ways Internally (inside) The egg is fertilised by sperm inside the female Mammals, birds, reptiles, insects, spiders Externally (outside) The egg is fertilised by a sperm outside the female The female lays the eggs and then the male fertilises them Fish and some amphibians Plants and fungi (pollen and spores)

Internal fertilisation Chances of fertilisation is increased Chances of survival is increased Zygote forms inside the female body External fertilisation Chances of fertilisation is reduced Produce many eggs as they are laid in water There is none or very little parental care

Parental cost Reproduction is costly. Individuals are limited in the degree to which they can devote time and resources to producing and raising their young, and such expenditure may also be detrimental to their future condition, survival, and further reproductive output. However, such expenditure is typically beneficial to the offspring, enhancing their condition, survival, and reproductive success

Parental care Parental investment can be provided by the female (female uniparental care), the male (male uniparental care), or both (biparental care). Parents are naturally selected to maximise the difference between the benefits and the costs, and parental care will tend to exist when the benefits are substantially greater than the costs

Fast versus slow Fast reproductive strategies are known as R – strategies Slow reproductive strategies are called the K - strategy

r – selected organisms Unstable environment, density independent Small size of organism Energy used to make each individual is low Many offspring are produced Early maturity Short life expectancy Each individual reproduces only once Type III survivorship pattern in which most of the individuals die within a short time but few live much longer

K – selected organisms Stable environment, density dependent interactions Large size of organisms Energy used to make each individual is high Few offspring are produced Late maturity, often prolonged period of parental care Long life expectancy Individuals can reproduce more than once in their lifetime Type I or II survivorship pattern in which most individuals live near the maximum life span

Type I curves high survival in early and middle life, followed by a rapid decline in survival in later life. They are typical of species that produce few offspring but care for them well, including humans and many other large mammals. Type II curves are an intermediate between Types I and III, where roughly constant mortality rate experienced regardless of age. Some birds and some lizards. Type III curves, the greatest mortality experienced early in life, with relatively low rates of death beyond this. Typical of species that produce a large number of offspring. This includes most marine invertebrates e.g. oysters  (millions of eggs, but most larvae die from predation or other causes) those that survive long enough to produce a hard shell live relatively long.

Reproductive strategies Reproductive strategies include monogamy and polygamy One mating partner versus many mating partners

Monogamy When two animals mate exclusively with each other or have only one partner

Polygamy When animals mate with multiple different partners Polygyny – when one male mates with multiple females Polyandry – when one female mates with multiple males

Courtship Courtship in animals is the behaviour by which different species select their partners for reproduction

Sexual dimorphism The differences in appearance between males and females of the same species, such as colour, shape, size, and structure

Sexual dimorphism Produced as a result of sexual selection over many generations

Male – male rivalry Large size or weaponry increases access to females through conflict. Some males act as sneakers to reproduce.

Sexual dimorphism Females are generally inconspicuous Males have more conspicuous marking, structures and behaviours

Female choice Females will assess ‘honest’ signals of the fitness of males? Fitness can be good genes or low parasite burden?

Lekking species Taking part in a communal breeding display on a lek, usually birds. Hierachy is established Dominant males usually get to mate as females will choose them. Satellite males may interfere with process in hope of mating with disturbed females.

Reversed sexual dimorphism Reverse sexual dimorphism is the tendency for certain bird species to reverse the normal trend for the male to be larger than the female. It is particularly found in birds of prey, for example the peregrine falcon whose adult male weighs in at around 660g whereas the female is over 1kg. The physical size differential is also very obvious.

Successful courtship strategies Species specific sign stimuli An external sensory stimulus that triggers a fixed action pattern Fixed action pattern An instinctive behavioural sequence that is often very consistent within the species and almost inevitably runs to completion.

Imprinting A period of rapid learning that occurs during a brief receptive period, typically soon after birth or hatching It establishes a long-lasting behavioural response to a specific individual or object, as attachment to parent, offspring, or site. It is likely to influence mate choice later in life.