In June, Alberta’s ecosystems are alive with activity. Much of this activity is focused on one thing – reproduction. While some species are icons for long-term, loyal relationships such as the swan, there are a variety of courtship, reproductive, and young-rearing styles found in nature.
Read on to discover some fun facts on the sexual diversity that exists in the natural world.
Ruddy Duck - Polygyny and Nest Parasitism
Ruddy duck pair. Photo credit: Gerald Romanchuk
Ruddy ducks are some of the most enigmatic ducks that can be seen in our waterways. With their baby-blue bills and vertical tails, they stand out from the rest of the flock. When it comes to breeding, Ruddy ducks employ a strategy that is also unique.
Most duck species display seasonal monogamy, in which the females and males stick together to raise young during the breeding season. Geese and swans take that a step further, and often form pairs that last a lifetime, with the fathers being very involved in care of the goslings or cygnets as they mature.
Ruddy ducks are one of the few waterfowl species that will display polygamous behaviour, meaning that the males may mate with multiple females over the course of the breeding season. Females will also engage in nest parasitism, a breeding strategy that outsources the hard work of feeding hungry hatchlings. It may seem unfair to our moral sensibilities, but it’s a valid reproductive strategy – whatever helps get the young to maturity!
Garter Snakes - Copulatory Plugs and Female Mimics
Snakes emerge after hibernation. Photo credit: Greg Schechter
Garter snakes in cold climates hibernate in dens during cold prairie winters, and emerge in large numbers in the spring, with males emerging a few days before females. Multiple males attempt to mate with females, forming what’s known as “mating balls”. The male deposits a copulatory plug after mating with a female, the purpose of which has been hypothesized many times. It appears that it has both the function of preventing the female from mating again, and in ensuring that the male’s sperm stays put.
Another interesting reproductive strategy is that some male garter snakes disguise themselves as female mimics, known to snake biologists as “she-males”. By drawing males away from a female snake, a “she-male” can use other snakes to protect themselves from predators such as birds and help them warm up after a cold winter, while possibly giving themselves a greater chance of mating with the female.
White-throated Sparrow – Chromosome Evolution in Action
White-throated sparrows have a distinctive song, one of the most melodic in the spring chorus of birdsong. There’s another way these unassuming birds stand out: they have four “sexes”, rather than the typical two.
This topic has been the thesis of geneticists, but we’ll give a brief summary. These humble sparrows have four different chromosome arrangements that correspond to four distinct patterns of behaviour, and four distinct phenotypes (the external, visible traits informed by genetic makeup): there are both white-stripe and tan-stripe males, and white-stripe and tan-stripe females. Variations in the typical colours of any species are called “morphs”, but genetic research has confirmed that the differences are not just skin-deep for these unassuming but fascinating birds.
A white-striped and tan-striped white-throated sparrow, photographed by Gerald Romanchuk. White-striped individuals have more highly-contrasted head markings, with stark white and black stripes, and a well-defined yellow patch above the beak. Tan-striped individuals have a more “faded” appearance, with head markings that look more washed out with tan. The yellow patch is not as stark.
In terms of behaviour, each variation of the White-throated sparrow behaves in distinctive ways. For example, white-striped birds engage in aggressive territory defense, but the tan-striped birds are much more laid-back.
With these differences comes a biological truth: one individual can only mate with one quarter of the White-throated sparrow population. This case is very rare in nature, and the study of these birds provides a glimpse into evolution in action. There’s much more to this fascinating species’ story, which you can find here.
Homosexual Behaviour in Mammals - Evolutionary Advantages
A relatively recent research area of evolutionary biology is understanding homosexual behaviours that are common in the animal kingdom. Same sex activity has been recorded in 261 mammal species, plus many other species including birds, reptiles, and invertebrates. These behaviours tend to be displayed by species with intricate social structures. But, since homosexual behaviour doesn’t result in offspring, why do so many species engage in it?
A study in Nature Communications described that same-sex behaviour in some mammals is shown to increase social bonds and mitigate conflicts among individuals, which in turn can provide benefits such as protection of young and improving an individual’s fitness for reproduction later. However, in some cases these behaviours may be the result of mistaken identity and may occur alongside a male of a species killing another adult male.
Nonconforming Nature
Nearly everywhere you look, animal species have specialized approaches to reproduction and raising their young, including strategies that defy our conventional understanding of sexual behaviour and reproduction in humans. Evolutionary biologists and other scientists study these behaviours to uncover the puzzle of how we got to where we are today.
