After winning a 21st Century Research Grant last year, PhD student Simon recently gave an update on his research in the latest newsletter for the NZ Entomological Society:
New Zealand is home to four native species of fishing spider (Dolomedes), including two sister species: D. minor and D. aquaticus which are the focus of my PhD research. There is genetic evidence to show that these two species are undergoing introgression. Introgression is the movement of genes from one species to another, caused by the backcrossing of a hybrid specimen with its parent species. In the case of these spiders, the introgression is one-way (with hybrids only produced by the mating of D. aquaticus females and D. minor males) and geographically restricted to the lower South Island, despite the species co-occurring throughout the range of D. aquaticus.
The reasons for these limitations are currently unknown, but my work is investigating several hypotheses: 1) habitat use differs in the introgression zone, facilitating encounters between the two species; 2) variation in genital morphology (specifically variation in the retrolateral tibial apophysis (RTA)) limits their sperm transfer; 3) variation in courtship behaviour limits mating; 4) timings of reproductive maturity limit mating opportunities.
The preliminary results of my experiments suggest that the two species possess different mating behaviours and systems. For example, unmated D. aquaticus females rarely attack males, whereas D. minor females often attempt to cannibalise males who try and escape during extremely brief copulations. This divergence in mating behaviours could also have an impact on the introgression, as these could limit sperm transfer between the two species.
Hence, my aims are to investigate the morphological and/or behavioural barriers that limit the geographic range of the introgression, and restrict it to one-way (i.e.: what prevents D. aquaticus males mating with D. minor females).
I am grateful to have received funding from the New Zealand Entomological Society, via the 21st Anniversary Research Grant. These funds allowed me to travel to Southland to collect specimens of D. minor and D. aquaticus from within the introgression zone. Working in these locations was a key part of my research, not to mention a highly enjoyable part of my work so far.
These specimens were brought back live to Waikato (despite some concerns from aviation security), where they were used in extensive mating experiments. I am currently in the process of analysing the results of these experiments and how they fit into my wider PhD findings.
Additionally, I am also working to scan the male genitals of these spiders using micro-CT, to analyse the morphology of the RTA and the impact this could have on introgression.
I cannot wait until these analyses are complete so I can share my full finding with The Society and the scientific community.
Congratulations to Simon, who recently won a $4000 Sparling Travel Award to take a long-awaited trip to Germany next month. While there, Simon will present his research at the European Congress of Arachnology, then spend some time in Prof Peter Michalik’s lab at the University of Greifswald. In Peter’s lab Simon will learn how to create 3D models of spider palps (male genitalia) that he has recently been prepping for by scanning the spiders using a micro-CT machine. Once back in New Zealand, Simon will use these models to conduct geometric morphometric analyses, to understand how genital shape may limit or allow introgression (transfer of genes) between two co-existing species of fishing spiders.
Just out this week in Evolutionary Ecology is a special issue put together by Emma Sherratt (University of Adelaide) Erin McCullough (Clark University) and myself, where we collated 14 original papers on the ecological and evolutionary implications of allometry.
We were pleased to get contributions spanning all three levels of biological scaling: ontogenetic allometry (scaling across an individual’s development), static allometry (scaling among individuals of the same developmental stage), and evolutionary allometry (scaling among species). The papers also spanned a wide number of taxonomic groups from insects to reptiles, and used a diverse range of methological approaches to explore the importance of allometry in animal biology.
Thank you to my co-guest editors for putting up with my absence while I was off getting to know kid #2, all the authors who contributed their research to the edition, the reviewers who found time during a pandemic to critique the manuscripts, and to Chief Editor at Evolutionary EcologyMatt Symonds for the invite to put this together.
Our recent paper on a very cool spider that masquerades as bird-droppings has made the cover of Current Zoology.
In this study Yu Long, then a PhD student at Hubei University in China, combined field observations, field experiments and visual modelling to test whether Phyrnarachne ceylonica spiders aggressively mimics bird droppings in order to deceive potential prey. I was lucky to visit Xishuangbanna Tropical Botanic Garden in beautiful Yunnan in 2015 while I was a postdoc at the National University of Singapore working on jumping spiders. This is where I met Yu Long and was able to give him a hand searching for bird-dropping spiders in the undergrowth of the forest for his experiments.
During his field observations, Yu Long found that thespiders attracted as many fly and hymenopteran prey as nearby fresh bird droppings, and much more prey than a bare leaf. In the next stage of his project Yu Long either experimentally whitened or blackened the spiders to look at how this affected prey attraction rates. As predicted, prey was attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, by measuring the colour of the spiders and bird droppings, we were able to show that both of these objects can be seen by visiting fly and hymenopteran prey when contrasting against background leaves. However, the spiders and bird droppings were visually indistinguishable from each other when looking through the eyes of a fly or bee.
Together these findings suggest that insects attracted to spiders may misidentify the spiders as bird droppings, meaning that the spiders not only receive benefits of looking like bird poo to avoid being picked off by predators, but also use aggressive mimicry to lure unsuspecting prey looking for a pooey feed.
Just some of the fascinating invertebrates found in the Xishuangbanna Tropical Botanical Garden
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.
I’m (Chrissie) currently on parental leave caring for my new bubba Elliot, who was born at the end of September. We spent the first 6 weeks of Elliot’s life in lockdown as the Delta strain spread into the Waikato. Needless to say it was a challenging time with a very energetic 4 year old at home to entertain while we got to know our new pēpi and adjusted to the familiar exhaustion from sleep deprivation. We’re all doing very well though and enjoying having a new addition to our whānau.
Despite my absence, the Painting lab is still busy, with Michaela handing in her MSc thesis at the end of 2021, and Lara soon to complete in mid January. Simon has been having a productive field season collecting spiders to run his mating experiments, and has been lucky to visit some beautiful sites in the South Island despite COVID doing its best to thwart plans. Rene’s work on the effects of temperature on pollination behaviour has also been held up with last year’s lockdowns, but will be progressing again in the new year. Grant’s off on a very exciting adventure in the waters around Antarctica as a fishing observer, but will be back soon to continue his MSc.
I’ll be back in the office/lab in September 2022. Feel free to get in touch before then – I’m still keeping an eye on my emails in between baby cuddles and pottering about in the vege garden.
Congratulations to our very own Simon Connolly for recently winning the People’s Choice Award at the University of Waikato 3MT Doctoral finals! Simon was one of 10 finalists who gave captivating talks on their PhD research, and from the laughter and cheers of the audience it was very clear that Simon had done a great job of entertaining and informing the crowd.
If you’d like to hear Simon’s talk on his research into sexual cannibalism in New Zealand nursery web spiders, you can check out the You Tube recording below.
Congratulations to Dr Erin Powell, who has had not one but TWO papers out from her PhD research on the evolution and ecology of weapon polymorphic New Zealand harvestmen over the last few weeks!
First up you can read a beautiful natural history account describing the predators, diet and defense behaviours of the long-legged harvestmen (Neopilionidae) found in Aotearoa New Zealand, which was published recently in the Journal of Arachnology. The paper includes lots of great images showing off the various behaviours she describes in the paper so it makes for a really enjoyable read. It’s so great to see natural history being appreciated and published by society journals.
Erin also did a really neat set of observations and experiments on one species of harvestmen, Forsteropsalis pureora, where she investigated the rates of autotomy among males of different weapon morphs. Lots of different animals use autotomy as a defense strategy against predators, where they can shed a limb at a predetermined breakage point to give themselves a better chance to escape. Erin hypothesised that males employing scrambling tactics would have higher rates of predation exposure during mate searching compared to males with much larger weapons, that use female-defense tactics. This could manifest in higher rates of autotomy for scrambling males. However, the experiments showed that although there were really high rates of autotomy (54% of wild caught males had at least one leg lost!), there was no evidence of different autotomy rates between male morphs. Also, during predator simulation experiments there was no difference in whether males from different morphs would drop legs, or which leg they dropped. This was a really nice example of a study that investigates the potential costs of scrambling to find mates. That paper is out now in Animal Behaviour.
Calling all researchers who are interested in allometry, the study of how the traits of organisms scale with size. Dr Emma Sherratt and I are guest editing a special issue in Evolutionary Ecology which will focus on the evolutionary and ecological implications of allometry. We would love to see submissions on your favourite study organisms across a wide range of fields including sexual selection, behaviour, metabolic scaling, coevolution and beyond.
We particularly welcome student and early career researcher submissions, who get additional benefits to publishing at Evolutionary Ecology including a Springer book voucher and free open access of your publication for the first 8 weeks online.
Feel free to get in touch with Emma and I with pre-submission enquiries or go ahead and submit before 31st August 2021.
For more details on the special issue, check out the call for papers here.
After a year of cancelled or virtual meetings, the Painting lab crew were very excited to head off to Dunedin last week to attend the 69th NZ Entomological Society Conference hosted at the Otago Museum. For some of the students it was their very first scientific meeting, and a perfect opportunity to share research findings and ideas in a friendly, supportive environment.
As you can image, pretty much every entomologist in New Zealand was buzzing for the opportunity to hang out with their fellow bug nerds and talk science for a few days, so the conference ended up being fairly large for a local meeting – about 120 participants if I’m not mistaken!
All of the Masters students in the lab presented a poster on their research, with two of them receiving awards for their work. Grant Fale got 1st prize for best poster for his Masters research investigating the interactions between native bees and honey bees on mānuka flowers, while Rene Devenish won 2nd prize for her MSc research on the effects of temperature on the physiology and behaviour of pollinators.
Above: Rene with her prize winning poster on the effects of warming temperatures on the physiology and behaviour of pollinators (left), and Michaela with her poster outlining her research on the effects of population density on mating dynamics in giraffe weevils.
Simon gave an engaging talk on some of his preliminary findings from his field research and crossing experiments figuring out the mating system and dynamics of introgression in two Dolomedes fishing spiders. He also won a 21st Anniversary student research award to support his ongoing research, including some upcoming field trips to the deep south of NZ to find some introgressing spiders!
Thanks to the organising committee for a wonderful few days hearing about all the great entomological research going on in NZ, and to our national COVID response team for making it possible to meet in person during a pandemic.