Autumn is a time of change and opportunities, a season to face new challenges and experience new feelings and sensations. Autumn smells of rain, forests and wet soil. One can hear the whisper and the voice of the wind. And while the brown, ocher and yellow tones take over the trees and ground, the lights and colours of the sky reveal the most intense sunsets of the year. There’s a tense calm, as days get shorter and leaves fall, undressing the branches. The first snows and the impassible winter are expected.
In nature, autumn is also synonymous with long journeys, periods of rest and magnificent battles: the migration of cranes, bear hibernation or deer bellowing are examples of the remarkable natural events that take place during this season, which will mark the future of the individuals involved in these phenomena.
Sexual selection and mating are especially important, as most species experience oestrus in autumn, a few months before spring and summer, when environmental conditions are ideal to raise offspring. In order to reproduce, adults must first come out victorious of the many competitive interactions that occur during the breeding season, which we’ll delve into in this article.
- 1 Intraspecific competition during the breeding season
- 2 Competition before sexual selection and mating
- 3 Competition after copulation
Intraspecific competition during the breeding season
During the breeding season and during sexual selection, it’s common to see competition between males (disputes, fighting, displacement, etc.); interactions that can determine their ability to find a mate, their breeding success and, consequently, their capability to survive. If this competition isn’t settled or solved appropriately, the lives of the animals involved could be at risk.
In most cases, competitive interactions take place before copulation, when there’s a power struggle between the strongest animals in their quest to ‘obtain’ females and adequate territories. However, even after mating, this competitive relationship may continue in certain circumstances.
Competition before sexual selection and mating
The fighting, dispute and displacement episodes that occur between males before mating are referred to as ‘precopulatory competition’. We observe this type of competition when males, in their attempt to court and seduce females, have to fight other individuals in order to defend their potential sexual mates and an adequate territory. In this case, secondary sexual characteristics play a very important role, as they allow to properly assess fighting ability.
However, it’s also true that secondary sexual characteristics barely contribute to the survival of animals, and can even be counterproductive. For example, female cervids generally don’t have antlers and males only have them during breeding season, so antlers are of limited value to fight competitors or predators. Growing antlers every year also has a high metabolic cost (in the form of phosphorus and calcium salts) and requires a lot of energy.
The exhausting direct confrontations, even when results are favourable, can reduce the ability to succeed in future challenges, so other indicators are preferable. For example, in the case of deer, there’s a positive correlation between a male’s ability to fight and the number of bellows per minute during the bellowing season.
Competition after copulation
Apart from competition before copulation, there are also situations in which a competitive relationship is established after mating; this is what we call ‘postcopulatory competition’. Through this energic type of competition, males try to improve their odds of reproductive success. Another competitive interaction is when they try to prevent females fecundated by other males from successfully raising their offspring.
In any case, the males of different species resort to a variety of methods in order to reach their objectives. In the following paragraphs, we’ll learn about some of these methods and the different species that use them.
Constantly monitoring the female
Magpies are common birds that are easy to identify, a corvid that can be found in most of the Northern Hemisphere. The male, in order to ensure fertilisation, monitors the female closely after copulating, until she lays her eggs. In order to ensure the survival of their offspring, both parents look after and feed them until they fly for the first time, approximately one month after birth.
Through a series of mechanisms and systems, many insects are able to extract the spermatozoa deposited in the female’s body by other males. For example, the penis of male Odonata has a whip with ‘saw teeth’, which it uses to remove the sperm within the female’s spermatheca from previous copulation with other males.
A unique courtship that takes place after mating
The Ugandan kob is a large antelope that inhabits the savannahs of Central Africa – the characteristic white spot on its throat makes it easy to identify. It’s a polygynous species, a system in which males can monopolise large harems of females. The case of this ungulate is quite unique, as, after copulating, they resume courtship, which contracts the womb of the female, improving fertilisation.
Infanticide (predation on offspring)
Infanticide occurs when the predictable result is an increase in the reproductive success of the male. In other words, infanticide is advantageous for males when it resumes the female’s oestrus, making her receptive to mating.
Predation on offspring is relatively common in some species, but doesn’t happen more often because the death of a very large number of offspring is required for the female to resume her oestrus. As a lot of descendants have to die, this may put the survival of the population at risk.
Abortion as a defensive response
The females of certain species are sometimes able to induce their own abortion, due to a pheromonal effect known as the ‘Bruce effect‘, which is a result of the exposure to the scent of an unfamiliar male. Studies on rats have shown that when females smell the urine of an unfamiliar male, they abort in order to prevent a potential infanticide.
Translated by Carlos Heras