For Lifers - Love in the Animal Kingdom

Finding a mate in the animal kingdom is absolutely essential to a species’ long-term survival. Cerys Deakin is here to delve into the different mating techniques adopted throughout the animal kingdom and explain why each species adopts them.

Throughout the animal kingdom, the systems and methods selected to attract a mate are highly varied across species and taxonomic groups. Alongside this, mating systems are also varied, with species like albatross mating for life and others such as elephant seals mating with multiple females each breeding season. Each species exhibits a mating system that optimises breeding success and is likely the outcome of long-term, historical evolution that has prevailed due to factors like parental investment, long-term parental care, nest maintenance, etc.

So what are the different mating systems? Mating for life, also known as monogamy, is when two individuals of a species will court one another and then continue to only reproduce with one another for the rest of their lives. Polygyny is when one male will reproduce with multiple females each breeding season, and polyandry is when one female will mate with multiple males in one breeding season. In some species, the sexual roles are reversed, with females competing for males and the males investing greater parental care.

Monogamy

Monogamy is when two individuals of a species form a bond that is more than just reproduction. It is a social bond whereby those individuals will typically remain life partners. Monogamous individuals will spend significantly more time with each other than with others, only mating with each other and both investing in parental care when raising offspring.

Approximately 90% of all bird species are monogamous, in addition to some mice and reptile species. Research suggests that monogamy may have been adopted by species that experience ecological and behavioural problems. These include limited resource availability, small mate pools and territory defence behaviours. In birds, monogamy is likely adopted to maximise long-term reproductive success. Many birds will only produce one brood in a single breeding season, so having two parents to invest efforts, energy and resources into one brood will likely increase survival likelihood. Furthermore, when two individuals work together across multiple breeding seasons they become more experienced and therefore become better at reproducing and rearing broods to fledging.

Black-browed Albatross. Pic Credit: claudiafortgeblasen via Pixabay

Species Spotlight - Black-browed Albatross

The black-browed albatross is labelled as a model species for monogamy with individuals becoming life-long mates following courtships. These beautiful birds were brought to our screens by David Attenborough and have since been known for their partnerships and high parental investment in their young. Whilst there is evidence of divorce in this species, which can occur when more dominant males enter a group and force out those which are less dominant, they are particularly iconic because individuals will often find their way back to one another at the start of each new breeding season. The male and female will then both invest in the rearing and care of the young with the hope of optimising reproductive success. While albatross are known for their lifelong bond, climate change is pushing up rates of divorce and increasing stress levels in individuals. This gives conservationists even greater motivation to monitor and conserve this species.

Polygyny

Polygyny is the mating system whereby males will mate with multiple females in one breeding season, not committing to one individual. There is evidence to suggest that species that have evolved to have polygynous mating systems have done so to enhance reproductive success. Evidently this is species-specific, so it is unsurprising that this is not a common mating system for birds but is much more common for larger mammals.

So why has polygyny prevailed throughout evolution? Polygynous males will mate with multiple females throughout a breeding season, often consequently siring many offspring. This is beneficial for males because it means there is a higher chance that their genes will be passed on to the next generation. Alongside this, with this mating system, males will not invest in parental care and instead invest in territory defence.

Elephant Seals. Pic Credit: MartinFuchs via Pixabay

Species Spotlight - Elephant Seals

Elephant Seals are an iconic example of polygyny in the animal kingdom. Male elephant seals often referred to as ‘beach masters’ have control over multiple females. This is referred to as a harem. Prior to the breeding season, the males will compete for territory, following which they will monopolise the increased access to females within the territory. One beach master can be in control of a harem of up to 100 females. It has even been recorded that when harems rise too high, a dominant male will allow a younger male to be an ‘assistant beachmaster’ for his harem.

Polyandry

Polyandry is the opposite of polygyny and occurs when females mate with multiple males in a single breeding season. Polyandry has evolved to maximise female breeding success. By mating with multiple individuals, the female is able to ensure that (1) there will be offspring produced that year and (2) the female’s own genetics get passed onto the next generation. Polyandry is a common mating system adopted by females when there is limited access to mates in the surrounding area, or where having access to only low-quality males is costly. Polyandry ensures that even where there are low-quality males, females will pass on their genes to at least one of the multiple males they mate with.

Western Honey Bee. Pic Credit: xiSerge via Pixabay

Species Spotlight - Honey Bee

The honey bee offers a fantastic example of a polyandrous mating system. For this species, one female (the queen bee) will mate with multiple males (drone bees). For honey bees in particular, polyandry is ideal as it increases the genetic diversity of the worker bees and therefore promotes the ability to adapt to new diseases and risks that the colony may face.

About the Author

Cerys is a final year MSci Zoology student at the University of Exeter, with a keen interest in conservation and animal welfare. Cerys demonstrates her skills on her LinkedIn and over on her Instagram @cerys.hermione.photography