Foraging behavior and extended phenotype independently affect foraging success in spiders

Multiple phenotypic traits often interact with each other to determine an individual’s fitness. Behavioral and extended phenotypic traits, such as architectural constructions, can contribute to fitness in an integrated way. The goal of this study was to understand how the interaction between behavioral and extended phenotypic traits can affect foraging success. We tested this question using black widow spiders, where spiders that are aggressive in a foraging context tend to build more gumfooted silk lines that aid in prey capture, while non-aggressive spiders build webs with fewer gumfooted lines. We repeatedly assessed behavior and web structure to quantify relationships between these traits, and then allowed spiders to forage for live prey on their own web or the web of a conspecific that differed in structure. Thus, we assessed how varying combinations of behavior and web structure affect foraging success, and if correlational selection might act on them. We confirmed that aggressiveness and number of gumfooted lines are positively correlated and found that capture success increased with both aggressiveness and the number of gumfooted lines. Yet, we did not find any evidence for correlational selection: aggressiveness and number of gumfooted lines appeared to affect foraging success independently of each other. These findings highlight that a correlation between traits that contribute towards the same ecological function does not necessarily imply correlational selection. Taking advantage of the experimental convenience afforded by extended phenotypic traits can provide insight into the functional consequences of phenotypic variation within and between individuals.

Game of webs: species and web structure influence contest outcome in black widow spiders

Population-level trait variation within species plays an often-overlooked role in interspecific interactions. In this study, we compared among-individual variation in web phenotype and foraging behavior between native black widows (Latrodectus hesperus) and invasive brown widows (Latrodectus geometricus). We staged repeated contests whereby native widows defended their webs against intruders of both species to 1) investigate how trait variation mediates web contest outcome among native widows and 2) see whether widow behavior differs in response to an invasive spider. In only one trait, the average number of foraging lines, did black widows differ from brown widows. Black widow residents that built more structural lines were more likely to successfully defend their webs from conspecific intruders (i.e., be the sole spider remaining on the web postinteraction). This association between web structure and contest outcome did not exist in trials between black widows and invasive brown widows; however, in interspecific interactions, these same residents were more likely to have intruders remain on the web rather than drive them away. Surprisingly, brown widows did not usurp black widows. Brown widows were never observed signaling, yet black widow residents signaled equally to intruders of both species. Our results suggest that among-individual variation among native species can influence the response toward invasive competitors and outcome of these interactions.

Distribution and fertility of the spider Latrodectus tredecimguttatus (Rossi, 1790) (Aranei: Theridiidae) in the Odessa region (Ukraine)

Population dynamics of the black widow spider depends primarily on climatic conditions (short warm winter, wet spring, and hot summer cause an increase in individuals numbers) and secondary – depends on forage base and the number of enemies (parasitoid wasps). Therefore, constant monitoring of black widow spiders in the Odessa region is really important. This article provides data on distribution of the spider Latrodectus tredecimguttatus (Rossi, 1790) obtained in 2014‒2018 in the Odessa Region (Ukraine). Preliminary surveys were conducted in all districts of the region, and black widow spiders were registered in ten out of 26 districts (Artsyzsky, Bilhorod-Dnistrovsky, Bilyaevsky, Bolgradsky, Izmailsky, Kiliysky, Limansky, Ovidiopolsky, Reniysky, Tatarbunarsky). Mainly, the black widow spiders occurred in the southern districts of the region. Black widow spiders were found to be more common in ruderal habitats (54% of the total individuals collected) and rarer in agrocenoses (12%), saline marshes and steppe areas (17% each). The number of eggs and number of cocoons made by one female were counted. The number of eggs in one cocoon ranged from 276 to 458, and the number of cocoons woven by one female – from one to seven. In the study area, intensive cocoon making and egg laying by the black widow spiders was observed in early July; then the intensity decreased gradually in August. The largest number of the black widows’ cocoons was found in three southern districts of the Odessa Region (Bolgradsky, Izmailsky, and Reniysky). The largest number of eggs in one cocoon was registered in the Reniysky district while the smallest number of eggs was recorded in the Bilhorod-Dnistrovsky (613) and Bilyaivsky (903) districts. The largest average number of eggs laid by one female was fixed in Reniysky (2710) and Bolgradsky (2571) districts. Moreover, in these two districts located in the south of the Odessa Region, the largest number of the black widows’ nests was found. The smallest number of nests was recorded from three districts: Artsyzsky, Bilyayevsky and Limansky.

Posture controls mechanical tuning in the black widow spider mechanosensory system

Spiders rely on mechanical vibration sensing for sexual signalling, prey capture and predator evasion. The sensory organs underlying vibration detection, called slit sensilla, resemble cracks in the spider's exoskeleton, and are distributed all over the spider body. Those crucial to sensing web- and other substrate-borne vibrations are called lyriform organs and are densely distributed around leg joints. It has been shown that forces that cause bending at leg joints also activate these lyriform organs. Little is known of how the biomechanics of the body of a freely-suspended spider in its natural posture interact with vibrations introduced into the body and how this affects vibration perception. Female black widow spiders, in particular, have a striking body-form; their long thin legs support a large pendulous abdomen. Here, we show that in their natural posture, the large abdominal mass of black widow females, interacts with the spring-like behaviour of their leg joints and determines the mechanical behaviour of different leg joints. Furthermore, we find that adopting different body postures enables females to alter both the level and tuning of the mechanical input to lyriform organs. Therefore, we suggest that posture may be used to flexibly and reversibly focus attention to different classes or components of web vibration. Postural effects thus emphasize the dynamic loop of interactions between behaviour and perception, i.e. between 'brain' and body.