Aaron M. T. Harmer

Potential for pre‐release diet supplements to increase the sexual performance and longevity of male Queensland fruit flies

1 Recent studies have shown that continuous access to a protein source (yeast hydrolysate) can greatly enhance the sexual performance of male Queensland fruit flies (Bactrocera tryoni; ‘Q‐flies’). However, in Sterile Insect Technique programmes used to eradicate or suppress wild populations, mass‐reared Q‐flies are typically fed only sucrose and water for up to 2 days before release.

High-performance spider webs: integrating biomechanics, ecology and behaviour

Spider silks exhibit remarkable properties, surpassing most natural and synthetic materials in both strength and toughness. Orb-web spider dragline silk is the focus of intense research by material scientists attempting to mimic these naturally produced fibres. However, biomechanical research on spider silks is often removed from the context of web ecology and spider foraging behaviour. Similarly, evolutionary and ecological research on spiders rarely considers the significance of silk properties. Here, we highlight the critical need to integrate biomechanical and ecological perspectives on spider silks to generate a better understanding of (i) how silk biomechanics and web architectures interacted to influence spider web evolution along different structural pathways, and (ii) how silks function in an ecological context, which may identify novel silk applications. An integrative, mechanistic approach to understanding silk and web function, as well as the selective pressures driving their evolution, will help uncover the potential impacts of environmental change and species invasions (of both spiders and prey) on spider success. Integrating these fields will also allow us to take advantage of the remarkable properties of spider silks, expanding the range of possible silk applications from single threads to two- and three-dimensional thread networks.

Sperm storage and utilization in female Queensland fruit flies (Bactrocera tryoni)

Abstract Female animals that use sperm from a single mating to fertilize eggs over an extended period require efficient mechanisms for sperm storage and use. There have been few studies of these mechanisms in tephritid flies. Mating, copula duration, sperm storage and sperm usage patterns are assessed in an Australian tephritid, the Queensland fruit fly (Bactrocera tryoni; a.k.a. ‘Q‐fly’). In particular, the present study investigates whether each of these aspects of mating varies in relation to female size or male size, whether sperm storage patterns change over time after mating (1, 5, 10 and 15 days), and the relative roles of the ventral receptacle and the two spermathecae as sperm storage organs. Large females are more likely to mate than are small females, and are also more fecund in the first 5 days after mating. Females are more likely to store some sperm and, among those that store some sperm, store more sperm if their mate is large. Most sperm are stored in the spermathecae (median = 97%), often with high levels of asymmetry between the two spermathecae. Asymmetry of sperm storage is related to number of sperm stored, but not to male or female size. Total number of stored sperm declines over the 15 days after mating, but this decrease in sperm numbers only reflects changes in the spermathecae; numbers of sperm in the ventral receptacle remain unchanged over this period. As a consequence, the proportion of total sperm stored in the spermathecae declines relative to the ventral receptacle. These results are consistent with a system in which small numbers of sperm are maintained in the ventral receptacle for fertilizations, and are replenished by sperm from the spermathecae as required. Sperm distribution and usage patterns in Q‐flies are comparable with recent findings in medflies, Ceratitis capitata, but differ markedly from patterns found in several Anastrepha species.

Sperm storage and copulation duration in a sexually cannibalistic spider

Female St Andrew’s Cross spiders control copulation duration by timing sexual cannibalism and may thereby control paternity if cannibalism affects sperm transfer. We have investigated the effect of copulation duration on sperm transfer and documented sperm storage patterns when we experimentally reduced the ability of females to attack and cannibalise the male. Virgin males and females were paired and randomly allocated either to a control treatment, where females were allowed to attack and cannibalise the male during copulation, or to an experimental treatment, where females were unable to cannibalise the male. The latter was achieved by placing a paintbrush against her chelicerae during copulation. Our experimental manipulation did not affect copulation duration or sperm storage. However, the number of sperm stored by the female increased with copulation duration only if the male was cannibalised, suggesting that cannibalism increases relative paternity not only through prolonged copulation duration following a fair raffle model but also through the cannibalism act itself. Future studies should explore whether cannibalised males ejaculate more sperm or whether females selectively store the sperm of cannibalised males.

Taking it to extremes: what drives extreme web elongation in Australian ladder web spiders (Araneidae: Telaprocera maudae)?

Behavioural plasticity is important for maximizing fitness in variable environments. Orb web spiders, which rely on their webs being optimized for particular conditions, should benefit from plasticity in their web-building behaviours as prey and environmental conditions vary over time. Small-scale variation in the structure of webs results from spiders adjusting the web to suit local conditions. On the other hand, broader-scale variation in orb webs of different species, particularly in some more extreme web forms, can be attributed to evolved adaptations for catching specific prey types. Australian ladder web spiders, Telaprocera maudae, build extreme orb webs that are many times taller than wide and attached against tree trunks. The degree of web elongation is strongly negatively correlated with tree circumference. In this study we tested whether this extreme web form is a result of highly plastic web-building behaviour or whether it is an evolved trait. Spiders were allowed to build in frames of various diameters to control available horizontal space. We found that T. maudae built significantly more elongated webs when space was limited, but more ‘typical’, circular orb webs when space limitation was relaxed. These results indicate that the extremely elongated webs of these spiders are largely due to unprecedented plasticity in web-building behaviour. This allows spiders to maximize web area, and hence foraging potential, when building in space-limited microhabitats. These results are surprising as behavioural plasticity generally contributes to far more subtle variation in orb web structure.

Time-Pattern and Frequency Analyses of Sounds Produced by Irradiated and Untreated Male Bactrocera tryoni (Diptera: Tephritidae) During Mating Behavior

Abstract Behavior and sounds associated with mating of mass-reared irradiated and untreated (nonirradiated) Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) males were analyzed from synchronous acoustic and video records. The flies tested were from a population used in sterile release programs that help maintain fruit-fly-free areas in Australia. Males typically produce “calling,” “courtship,” and “copula” sounds as mating progresses. Calling sounds are variable-duration bursts of wing vibrations produced before the male orients toward the female. Rapid bursts of courtship sounds of relatively constant duration are produced after orientation toward the female. Copula sounds of variable amplitude and duration are produced after mounting. There was a significant negative correlation between courtship wingbeat frequency and wing width of untreated males, and those that copulated had a lower frequency than those that failed. Wingbeat frequencies in flight, calling, courtship, and copula sounds were significantly correlated within flies, possibly because they all are produced by the same flight motor, with amplitudes affected by the positioning of the wings relative to “stops” on the thorax. The temporal patterns of calling and courtship sounds differed significantly between irradiated and untreated males. Irradiation is known to damage insect central nervous system interneurons and thereby alter the coordination and timing of behavioral activities, but this is the first study identifying an effect of irradiation on tephritid calling and courtship sounds. Although differences in temporal patterns of calling and courtship sounds have potential to affect mating competitiveness, no differences were observed in proportions of irradiated and untreated males that copulated in the laboratory.

Elongated orb-webs of Australian ladder-web spiders (Araneidae: Telaprocera) and the significance of orb-web elongation

Many orb-web spiders build modified, asymmetrical orbs. Ladder-webs (a general term describing highly elongated orb-webs) are extreme examples of modified orbs built by several spider species in different families. Australian ladder-web spiders, Telaprocera (Araneidae), build highly elongated orbs consisting of a centralised orb-like portion with ladder extensions above and below. Webs are built exclusively on tree trunks, although most of the web is not in direct contact with the tree surface, as in some other ladder-web species. This study provides the first detailed description of the web structure, web-building behaviour and habitat preferences of Telaprocera spiders and discusses possible functions of this highly elongated orb-web form. The ladder-web of Telaprocera is probably an adaptation to building against trees, rather than the proposed moth specialisation function in some other ladder-web species. This has also been suggested for an African ladder-web spider Clitaetra irenae. Additionally, the web-building behaviour of Telaprocera spiders differs from that of the New Zealand ladder-web spider, Cryptaranea atrihastula, despite its remarkably similar web form.

Female song rate and structure predict reproductive success in a socially monogamous bird

Bird song is commonly regarded as a male trait that has evolved through sexual selection. However, recent research has prompted a re-evaluation of this view by demonstrating that female song is an ancestral and phylogenetically widespread trait. Species with female song provide opportunities to study selective pressures and mechanisms specific to females within the wider context of social competition. We investigated the relationship between reproductive success and female song performance in the New Zealand bellbird (Anthornis melanura), a passerine resident year round in New Zealand temperate forests. We monitored breeding behavior and song over three years on Tiritiri Matangi Island. Female bellbirds contributed significantly more towards parental care than males (solely incubating young and provisioning chicks at more than twice the rate of males). Female song rate in the vicinity of the nest was higher than that of males during incubation and chick-rearing stages but similar during early-nesting and post-breeding stages. Using GLMs, we found that female song rates during both incubation and chick-rearing stages strongly predicted the number of fledged chicks. However, male song rate and male and female chick provisioning rates had no effect on fledging success. Two measures of female song complexity (number of syllable types and the number of transitions between different syllable types) were also good predictors of breeding success (GLM on PC scores). In contrast, song duration, the total number of syllables, and the number of ‘stutter’ syllables per song were not correlated with fledging success. It is unclear why male song rate was not associated with reproductive success and we speculate that extra-pair paternity might play a role. While we have previously demonstrated that female bellbird song is important in intrasexual interactions, we clearly demonstrate here that female song predicts reproductive success. These results, with others, highlight the need for a change in how we view the significance of female secondary sexual traits; traits long underestimated due to a focus on male song.

Large orb-webs adapted to maximise total biomass not rare, large prey

Spider orb-webs are the ultimate anti-ballistic devices, capable of dissipating the relatively massive kinetic energy of flying prey. Increased web size and prey stopping capacity have co-evolved in a number orb-web taxa, but the selective forces driving web size and performance increases are under debate. The rare, large prey hypothesis maintains that the energetic benefits of rare, very large prey are so much greater than the gains from smaller, more common prey that smaller prey are irrelevant for reproduction. Here, we integrate biophysical and ecological data and models to test a major prediction of the rare, large prey hypothesis, that selection should favour webs with increased stopping capacity and that large prey should comprise a significant proportion of prey stopped by a web. We find that larger webs indeed have a greater capacity to stop large prey. However, based on prey ecology, we also find that these large prey make up a tiny fraction of the total biomass (=energy) potentially captured. We conclude that large webs are adapted to stop more total biomass, and that the capacity to stop rare, but very large, prey is an incidental consequence of the longer radial silks that scale with web size.

Functional diversity of ladder-webs: moth specialization or optimal area use?

Abstract Ladder-webs are built by several orb-web spider species and can be divided into two main groups based on the microhabitat in which they are built, either in open spaces (aerial) or against tree trunks (arboricolous). In Australian ladder-web spiders, Telaprocera, the elongated webs are a highly plastic behavioral response to building in space-limited conditions against tree trunks, while the aerial ladder-webs of Scoloderus are an adaptation for catching moths. However, the relative importance of moth capture in the construction of elongated webs in arboricolous spiders cannot be determined with existing data. We here present observational and experimental data concerning prey capture in the arboricolous spiders T. maudae Harmer & Framenau 2008 and T. joanae Harmer & Framenau 2008. We found that moths make up only a small fraction (< 4%) of the diet of Telaprocera spiders and that the proportions of major prey orders in webs are representative of available prey. Our experiments indicate that these webs do not function well at retaining moths. However, further data are required before more definite conclusions can be drawn regarding whether these webs are more effective at retaining moths than standard orb-webs.