Sperm Selection and Plasticity

Physiologic polyspermy, the regular and normal occurrence of multiple sperm penetration of the ovum, is a requirement in birds for normal egg fertilization and embryo development. The number of sperm trapped between the by the membranes surrounding the yolk after fertilization is directly correlated with the number of sperm that have penetrated the ovum. This number is positively related to the egg size, but there is significant variation both within and across species with similar sized eggs that remains to be explained. The number of sperm reaching the egg is heavily influenced by post copulatory selection, often reducing several million... [Read More]

Jewellery Fishing to Extinction?

The genetic relationships of Nautilus

People are beginning to care more about where their products come from, and the impact their choices have on animals and the environment. This includes the indirect impact of products that we buy, such as jewellery. One group of animals that is greatly affected by the jewellery industry is the cephalopod genus Nautilus. These animals are fished for their beautiful shells that are used as pendants and statement pieces, whilst the inside of their shell can be used as a pearl substitute. Nearly 1.7 million Nautilus shell products were imported into America over the past 16 years. <img src="http://ausevo.github.io/img/blog/naut1.png" alt=""... [Read More]

No Cost of Mating for Male Neriid Flies?

Male reproductive output can be limited by sperm production in that frequent mating can decrease sperm stores in many species. This can result in a decrease in fertilisation potential and in offspring sired. However, other costs of frequent mating to male reproductive performance are often overlooked, including trans-generational paternal effects on offspring viability and condition. Proteins and peptides found in the ejaculate can influence male reproductive performance by affecting fertilisation success and by altering female physiology to increase reproductive output and paternity share. It has also been demonstrated that components in the ejaculate likely influence trans-generational paternal effects on offspring... [Read More]

The Ties that Bind

Grand-parental qualities affect the lifespan of descendants

What if the quality of your parents’ diet could have an effect on your lifespan? Parental age has been shown to affect offspring fitness in surprising ways. Generally speaking, offspring produced by older parents do not live as long and little is known as to why this occurs. One proposed mechanism is non-genetic inheritance (i.e., inheritance of traits not produced through genetic coding). Once rejected by the modern synthesis, non-genetic inheritance has enjoyed a renaissance with many empirical studies showing a variety of underlying mechanisms that operate alongside Mendelian inheritance. The Neriid fly... [Read More]

Sex and steroids

An agricultural contaminant impacts sexual selection in a freshwater fish

Sexual selection is a powerful evolutionary driver. It describes the reproductive advantage that attractive individuals have over their less desirable conspecifics, and is responsible for some of the most spectacular traits seen in nature. In most organisms males compete for the attention of females, and although the traits that females find attractive vary greatly between species, they all have one thing in common: they provide an honest indicator of a male’s quality. As a result, females gain an advantage from mating with these attractive males - either direct benefits such as increased parental care, or indirect genetic benefits for her... [Read More]

Coevolution in action

Defences against brood parasitism in new and old hosts of the eastern koel

Avian brood parasitism is a model example of coevolution, yet measuring the rate at which coevolution takes place between a brood parasite and its host is difficult, as parasites rarely switch to completely naïve hosts. In Australia, the brood parasitic Eastern Koel (Eudynamis orientalis) recently switched to a new host, the Red Wattlebird (Anthochaera carunculata), providing a rare opportunity to observe coevolution in action. We compared the evolution of defences in the new host with those of traditional hosts at two sites with different durations of parasitism by the koel: Sydney (~37 years) and Canberra (~7 years). Specifically, we tested... [Read More]

Reproductive Ageing and Individual Condition

Ageing, the decline in performance with increasing age, is often associated with a decline in reproductive performance, referred to as reproductive ageing. Despite important fitness consequences of this trait, why it varies within species remains poorly understood. At least some of this variation can be explained by variation in resource acquisition. Also called “condition”, this determines not only energy budget, but also can determine investment in reproduction. For example, for males of many species, high condition (usually larger) individuals often express exaggerated physical traits such as sexual ornaments or weapons, or are more aggressive. Investment in these traits may increase... [Read More]

From being a lamb to becoming a wolf

No matter whether you are a human, a bird or a fish, growing up is not an easy feat. Not only does growing up involve drastic changes in morphology, physiology and behaviour, it usually also signifies the most vulnerable time in an animal’s life. Consequently, many animals rely on strategies such as camouflage and mimicry to make it past their early life stages. The dusky dottyback, Pseudochromis fuscus, is a small coral reef fish (~ 8 cm) that can be found in various different colours (yellow, brown, grey and pink) across the Indo-Pacific. Dottybacks are vicious predators that consume up... [Read More]

Major Urinary Proteins as a Sexual Signal in Rats

What does the tail of a peacock, the antlers of a deer and pheromones in rat urine have in common? These are sexually dimorphic traits - primarily seen in males- and have evolved with the sole purpose to attract mates. Sexual selection gives rise to traits that aim to maximize reproductive success, often at the expense of survival due to the demands it places on the signaler. An individual’s fitness determines how it copes with this cost, leading to variation in strength of sexual signal which females use to choose a mate. In rodents, such social information can be relayed... [Read More]

Sexual Selection and Sperm-egg Interactions in a Marine Broadcast Spawner

Sexual selection, one of Darwin’s seminal theories, has become a very familiar evolutionary force. Essentially, it occurs when some individuals are more successful in reproduction, either because they are better at competing for access to mates or are more attractive to potential mates. Perhaps less widely realised outside of evolutionary biology is that sexual selection continues after mating, with sperm from multiple males often competing for fertilisations, and females (or their eggs) exhibiting ‘cryptic’ choice for preferred sperm. Although these gamete interactions and their evolutionary outcomes are crucial for a wide range of taxa, it is often very difficult to... [Read More]

Female Singers are Colourful

Elaborate plumages and songs in male birds provide classic evidence for Darwinian sexual selection, but the possession of elaborate traits by females is less well understood. Female birdsong has recently been revealed as a taxonomically-widespread trait within the songbirds (oscine Passerines), and female-specific functions of song and plumage ornamentation have been resolved for a growing number of species. If elaborated female traits are adaptive, this raises the question: what is the evolutionary relationship between female song and plumage colour elaboration? Do the two traits trade off against each other, or evolve in concert? <span... [Read More]

Seeing Double

Using both lenses and mirrors to see

A newly discovered fish is just the second vertebrate known to use both lenses and mirrors to focus light in the eye. The eyes of the glasshead barreleye, Rhynchohyalus natalensis, are described by an international team of researchers, including some from the University of Western Australia and the University of Queensland, in a paper published in the Proceedings of the Royal Society. The glasshead barreleye is a denizen of the mesopelagic zone, the twilight ocean, where downwelling sunlight is too dim for photosynthesis. Barreleye fish hang in the water with large, cylindrical eyes pointed at the surface, waiting for... [Read More]