Beyond the prey: male spiders highly invest in silk when producing worthless gifts

In the spider Paratrechalea ornata, males have two gift-giving mating tactics, offering either a nutritive (prey) or a worthless (prey leftovers) silk wrapped gift to females. Both gift types confer similar mating success and duration and afford males a higher success rate than when they offer no gift. If this lack of difference in the reproductive benefits is true, we would expect all males to offer a gift but some males to offer a worthless gift even if prey are available. To test this, we allowed 18 males to court multiple females over five consecutive trials. In each trial, a male was able to produce a nutritive gift (a live housefly) or a worthless gift (mealworm exuviae). We found that, in line with our predictions, 20% of the males produced worthless gifts even when they had the opportunity to produce a nutritive one. However, rather than worthless gifts being a cheap tactic, they were related to a higher investment in silk wrapping. This latter result was replicated for worthless gifts produced in both the presence and absence of a live prey item. We propose that variation in gift-giving tactics likely evolved initially as a conditional strategy related to prey availability and male condition in P. ornata. Selection may then have favoured silk wrapping as a trait involved in female attraction, leading worthless gift-giving to invade.

ERYTHROLAMPRUS MILIARIS (LINNAEUS, 1758) (SQUAMATA: DIPSADIDAE) A NEW PREY ITEM OF TROPIDURUS TORQUATUS (WIED-NEUWIED, 1820) (SQUAMATA: TROPIDURIDAE) IN SOUTHEASTERN BRAZIL

Although ophiophagy is not a well-known event among neotropical lizards, occasional snake predation events have been reported for some species. For Tropidurus torquatus only one record of predation on Phalotris matogrossensis is currently known. Here we report the second record of ophiophagy in Tropidurus torquatus, adding a new prey item to its known diet, and we provide a review of vertebrate prey consumed by this enigmatic lizard species. Although when compared to other lizard species, T. torquatus has a substantial number of records documenting the predation of small vertebrates, these records are occasional and are likely the result of opportunistic events.

Predation of the Japanese keelback (Hebius vibakari Boie, 1826) by the Slender racer (Orientocoluber spinalis Peters, 1866)

Background The Slender racer (Orientocoluber spinalis Peters, 1866) has recently been reclassified to the new genus Orientocoluber from Hierophis. Ecological knowledge of this species is limited due to its highly mobile behavior. On 17 July 2020, we captured a female O. spinalis on Oeyeon Island, Boryeong-si, Republic of Korea, and collected its feces for a diet analysis. We observed snake scales from the collected feces and subsequently determined the prey species through morphological and molecular methods. Results We initially hypothesized that the extracted fecal sample scales belonged to H. vibakari, due to their thin keel and rhombus shape. We also amplified H. vibakari DNA from the extracted fecal sample using Illumina sequencing methods. Our morphological and molecular results suggest that O. spinalis predates H. vibakari on Oeyeon Island. Conclusion This is the first report of O. spinalis predating another snake species, ophiophagy, and implies that H. vibakari may be a crucial prey item for O. spinalis on Oeyeon Island.

Differing impacts of two major plant invaders on urban plant-dwelling spiders (Araneae) during flowering season

Plant invasions can have major impacts on ecosystems and influence global species diversity. In Central Europe, Himalayan balsam (Impatiens glandulifera) and American goldenrods (Solidago canadensis and S. gigantea) are important invaders often establishing dense and homogeneous stands, especially in urban and other disturbed habitats. We investigated their impacts on plant-dwelling spiders (abundance, family structure, guild structure) and potential spider prey items during flowering season within an urbanized landscape using a paired design comparing invaded and native reference vegetation plots. In general, flowering American goldenrods and Himalayan balsam had no significant impacts on the spider family composition. Invasion of American goldenrods further had no effect on total spider abundance and potential prey item abundance. In contrast, goldenrods showed a significantly increased crab spider (Thomisidae) abundance while being less inhabited by web builders. Himalayan balsam negatively influenced free hunters and running crab spider (Philodromidae) abundance, while we found no effects on other groups and total spider abundance. For Himalayan balsam, potential prey item abundance was higher than in native vegetation stands. Notwithstanding that our results only represent a snapshot of the system, they suggest that large-scale removal of urban goldenrod stands during flowering season might negatively influence local spider abundance, especially of crab spiders. Management efforts should therefore be accompanied by compensation measures to avoid disruptive effects on local plant-dwelling spider communities.

Predation and prey-caching of Eastern Water Skinks Eulamprus quoyii by nesting Nankeen Kestrels Falco cenchroides in eastern New South Wales

The breeding diet of a pair of Nankeen Kestrels Falco cenchroides nesting in Beresfield, eastern New South Wales, in 2020 was investigated. By individual prey species, the diet comprised 61.3% reptiles (including two prey species not previously recorded in the Nankeen Kestrel diet—Eastern Water Skink Eulamprus quoyii and most likely Southern Rainbow Skink Carlia tetradactyla), 9.7% birds (including a new prey species—Superb Fairy-wren Malurus cyaneus), 6.4% invertebrates (two crickets: Grylloidea), 3.2% mammals (one House Mouse Mus musculus) and 19.4% unidentified prey items (percentages by number). During 31.5 h of observations, the male delivered 22/31 prey items (71%) and the female delivered 9/31 prey items (29%) to the nest tree. The average delivery rate over the entire nestling period was one prey item per hour. Prey-caching, whereby the female stored lizards in the fork of a tree and later retrieved them and fed them tothe single nestling, was observed. Further studies are needed to obtain well-documented accounts of prey-caching by Australian falcons.

Sand throwing in a pit-building antlion larva from a soil mechanical perspective

Sandy pitfall traps are an elaborate construction to capture prey and antlions are well-known representatives of this predation technique. From a soil mechanical perspective, antlions exploit the interactions between the particles of their habitat and engineer a stable trap. This construction is close to the unstable state, where a prey item will immediately slide towards the center - towards the ambushing antlion - when accidently entering the trap. This method is efficient, but requires permanent pit maintaining. According to the present knowledge, antlions throw sand at their prey, to distract it, and/or cause sand slides towards the center of the pit. Using sand throwing and escape experiments, as well as finite element analysis, we supported this hypothesis. Furthermore, we added new hypothesis about maintaining the pitfall trap. We showed that sand that accumulates in the center of the pit will be continuously removed, which lead to the slope maintenance close to an unstable condition. This avoids self-burial of the antlion, as well as decreasing the chance of prey item escapes by keeping the slope angle steep. This demonstrates the interaction of an insect larva with its abiotic environment from a novel perspective and adds further insights into longstanding entomological hypotheses.

Interannual variability in the lipid and fatty acid profiles of east Australia-migrating humpback whales (Megaptera novaeangliae) across a 10-year timeline

Southern hemisphere humpback whales are classified as high-fidelity Antarctic krill consumers and as such are vulnerable to variability and long-term changes in krill biomass. Evidence of heterogeneous feeding patterns of east coast of Australia migrating humpback whales has been observed, warranting a comprehensive assessment of interannual variability in their diet. We examined the lipid and fatty acid profiles of individuals of the east coast of Australia migrating stock sampled between 2008 and 2018. The use of live-sampled blubber biopsies showed that fatty acid profiles varied significantly among all years. The two trophic indicator fatty acids for Antarctic krill, 20:5ω3 and 22:6ω3 remained largely unchanged across the 10-year period, suggesting that Antarctic krill is the principal prey item. A distance-based linear model showed that 33% of the total variation in fatty acid profiles was explained by environmental variables and climate indices. Most of the variation was explained by the Southern Annular Mode (23.7%). The high degree of variability observed in this study was unexpected for a species that is thought to feed primarily on one prey item. We propose that the observed variability likely arises from changes in the diet of Antarctic krill rather than changes in the whale’s diet.

The Evolutionary Continuum of Functional Homodonty to Heterodonty in the Dentition of Halichoeres Wrasses

Synopsis Vertebrate dentitions are often collapsed into a few discrete categories, obscuring both potentially important functional differences between them and insight into their evolution. The terms homodonty and heterodonty typically conflate tooth morphology with tooth function, and require context-dependent subcategories to take on any specific meaning. Qualifiers like incipient, transient, or phylogenetic homodonty attempt to provide a more rigorous definition but instead highlight the difficulties in categorizing dentitions. To address these issues, we recently proposed a method for quantifying the function of dental batteries based on the estimated stress of each tooth (inferred using surface area) standardized for jaw out-lever (inferred using tooth position). This method reveals a homodonty–heterodonty functional continuum where small and large teeth work together to transmit forces to a prey item. Morphological homodonty or heterodonty refers to morphology, whereas functional homodonty or heterodonty refers to transmission of stress. In this study, we use Halichoeres wrasses to explore how a functional continuum can be used in phylogenetic analyses by generating two continuous metrics from the functional homodonty–heterodonty continuum. Here we show that functionally heterodont teeth have evolved at least 3 times in Halichoeres wrasses. There are more functionally heterodont teeth on upper jaws than on lower jaws, but functionally heterodont teeth on the lower jaws bear significantly more stress. These nuances, which have functional consequences, would be missed by binning entire dentitions into discrete categories. This analysis points out areas worth taking a closer look at from a mechanical and developmental point of view with respect to the distribution and type of heterodonty seen in different jaws and different areas of jaws. These data, on a small group of wrasses, suggest continuous dental variables can be a rich source of insight into the evolution of fish feeding mechanisms across a wider variety of species.

Prey items of some amphibians and reptiles in Phu Khieo–Nam Nao Forest Complex, northeastern Thailand

Thongproh P, Chunskul J, Rongchapho P, Chuaynkern C, Chuaynkern Y, Srisonchai R, Saengsri C, Aonpime P, Phochayavanich R, Kanishthajata P, Phusaensri S, Prompalad S, Tongpun S, Arkajag J, Duengkae P. 2020. Prey items of some amphibians and reptiles in Phu Khieo–Nam Nao Forest Complex, Northeastern Thailand. Biodiversitas 21: 4124-4130. We reported prey items for two amphibians (Fejervarya limnocharis and Sylvirana nigrovittata) and three reptiles (Hebius sp., Bungarus candidus and Xenopeltis unicolor) from several areas of Phu Khieo–Nam Nao Forest Complex (northeastern Thailand) based on direct observation method. Fejervarya limnocharis (Anura: Dicroglossidae) consumed Amynthas sp. (Clitellata: Megascolecidae) in Nam Nao National Park (Phetchabun Province), while Sylvirana nigrovittata (Anura: Ranidae) consumed Megaustenia sp. (Gastropoda: Ariophantidae) in Phu Long Forest (Chaiyaphum Province). Consumption of snails in Sylvirana nigrovittata was documented as the first report on this prey item for the species. In Phu Luang Wildlife Sanctuary (Loei Province), Hebius sp. (Serpentes: Colubridae) consumed Fejervarya limnocharis while Bungarus candidus (Serpentes: Elapidae) consumed Argyrophis muelleri (Serpentes: Typhlopidae). Xenopeltis unicolor (Serpentes: Xenopeltidae) consumed Glyphoglossus molossus (Anura: Microhylidae) in Phu Wiang National Park (Khon Kaen Province).