We recently celebrated the completion of the first two MSc students based in the Invertebrate Ecology lab at the University of Waikato – an epic achievement given the current, ah, world situation that doesn’t need an introduction. Despite the challenges that Michaela and Lara faced while trying to do research during a pandemic, they both pulled off interesting, creative and novel research.
Michaela’s thesis focused on sexual selection in the New Zealand giraffe weevil by looking at the effects of population density on mating dynamics and the size-dependent investment into pre- and post-copulatory traits. Michaela did lots of fine-scale morphometrics to look at how males of different sizes invest into traits like sperm, testes and aedeagus size, as well as sperm volume. Here, the main findings were that postcopulatory traits showed negative allometry, demonstrating that small males have relatively long sperm and big testes compared to large males. This investment may mean that small males invest more into traits that give them a better chance at fertilising a female’s eggs, rather than weaponry that would help them gain mating opportunities. This makes sense when considering the behavioural ecology of the species where small males sneak copulations while large males rely on fighting tactics. However, Michaela also found that sperm concentration was much higher in large males, which was surprising given that theory predicts that small males at higher risk of sperm competition should invest more into ejaculates. Michaela’s findings raise lots of questions about the interaction between pre- and post-copulatory traits in the NZ giraffe weevils, some of which we hope to solve using behavioural observations paired with paternity analyses.
Michaela was also able to tackle the question of how population density interacts with body size to influence mating success across male giraffe weevils. Using a large dataset of field observations that Chrissie collected during her PhD way back in 2011/2012, Michaela was able to confirm that body size in conjunction with temporal fluctuations in population density and sex ratio have an important effect on the mating dynamics of giraffe weevils within a natural population.
Lara’s thesis also investigated contest behaviour, but used Teleogryllus commodus crickets to tease apart factors that affect decision making during fights. Game theory has had a long history of application to animal contests, but many previous studies that have tried to determine how individuals decide when to withdrawal from a contest have found inconclusive results. Lara used a series of elegant lab experiments to address whether there was variation among individuals in the assessment strategy employed, and whether personality could explain this population variation. In addition she also looked at whether the individuals themselves switch their assessment strategy part-way through a contest, which has been found in several previous studies.
Firstly, Lara set up a series of four behavioural assays that were used to determine if this cricket shows evidence of personality. This meant LOTS of assays because each cricket needed to do all four assays three times each, and she had lots of different individuals. A whole lot of lab work later showed that T. commodus indeed shows evidence of personality, where individuals showed consistent reactions to different situations like being put into a novel environment or faced with a simulated predator. However, she didn’t find evidence of a behavioural syndrome that linked behaviour across each assay type.
To figure out whether there was variation among individuals in the type of assessment strategy used during fights, Lara set up another series of behavioural experiments. She first ran a set of males through three bouts of a novel environment assay to quantify repeatability of exploratory behaviour for each individual. After that, each focal male was paired with 5 different opponents in a series of repeated contests that were then analysed using a new framework proposed by Kenneth Chapin and colleagues in their recent paper in Behavioral Ecology. Lara found evidence of variation in assessment strategy across the population, with some individuals using self assessment, and others using mutual assessment. She also found that individuals are likely to be able to switch assessment strategy as contests escalate to more intense physical fights. However, there was no evidence that personality affected the strategy that individuals used during fights.
One of the most satisfying aspects of Lara’s research was that it was inspired by discussions in the postgraduate Animal Behaviour class that I convene. Rene (also in the lab!) chose to discuss an interesting paper by Gabriel Lobregat and colleagues that looked at assessment strategy switching during contests. This led to further chats between Lara and I and a whole new project came out of it! One of the best part of teaching a postgrad paper is the chance to read more widely across the behaviour literature and be inspired to chase new project ideas, and it’s great to see what students choose to bring to discuss.
Thanks a lot to our collaborators across the globe who we worked closely with on these projects, who are all super clever early career researchers! Big ups to Dr Ummat Somjee (Smithsonian Tropical Research Institute), Dr Zac Wylde (University of New South Wales), Dr Chia-chen Chang (UC Davis), and Dr Paulo Enrique Cardoso Peixoto (Universidade Federal de Minas Gerais).