The value of spatial experience and group size for ant colonies in direct competition

Animals often search for food more efficiently with experience.However,the contribution of experience toforaging success under direct competition has rarelybeen examined.Here we used colonies of an individually foraging desert ant to investigate the value of spatial experience.First,we trained worker groups of equal numbers to solve either a complex or a simple maze.We then tested pairs of both groups against one another in reaching a food reward.This task required solving the same complex maze that one of the groups had been trained in,to determine which group would exploit better the food reward.The worker groups previously trained in the complex mazes reached the food reward faster and more of these workers fed on the food than those trained in simple mazes,but only in the intermediate size group.To determine the relative importance of group size versus spatial experience in exploiting food patches,we then tested smaller trained worker groups against larger untrained ones.The larger groups outcompeted the smaller ones,despite the latter's advantage of spatial experience.The contribution of spatial experience,as found here,appears to be small,and depends on group size:an advantage of a few workers of the untrained group over the trained group negates its benefits.

The combined role of visual and olfactory cues in foraging by Cataglyphis ants in laboratory mazes

Foragers use several senses to locate food,and many animals rely on vision and smell.It is beneficial not to rely on a single sense,which might fail under certain conditions.We examined the contribution of vision and smell to foraging and maze exploration under laboratory conditions using Cataglyphis desert ants as a model.Foraging intensity,measured as the number of workers entering the maze and arriving at the target as well as target arrival time,were greater when food,blue light,or both were offered or presented in contrast to a control.Workers trained to forage for a combined food and light cue elevated their foraging intensity with experience.However,foraging intensity was not higher when using both cues simultaneously than in either one of the two alone.Following training,we split between the two cues and moved either the food or the blue light to the opposite maze corner.This manipulation impaired foraging success by either leading to fewer workers arriving at the target cell(when the light stayed and the food was moved)or to more workers arriving at the opposite target cell,empty of food(when the food stayed and the light was moved).This result indicates that ant workers use both senses when foraging for food and readily associate light with food.

Consistent differences in foraging behavior in 2 sympatric harvester ant species may facilitate coexistence

The co-occurrence of 2 similar species depends on their ability to occupy different ecological niches. Here, we compared the consistency of different aspects of foraging behavior in 2 cooccurring harvester ant species （Messor ebeninus and Messor arenarius）, under field conditions. The 2 species are active concomitantly and display a similar diet, but M. arenarius features smaller colonies, larger workers on average, and a broader range of foraging strategies than M. ebeninus. We characterized the flora in the 2 species＇ natural habitat, and detected a nesting preference by M. arenarius for more open, vegetation-free microhabitats than those preferred by M. ebeninus. Next, we tested the food preference of foraging colonies by presenting 3 non-native seed types. Messor arenarius was more selective in its food choice. Colonies were then offered 1 type of seeds over 3 days in different spatial arrangements from the nest entrance （e.g., a seed plate close to the nest entrance, a seed plate blocked by an obstacle, or 3 plates placed at increasing distances from the nest entrance）. While both species were consistent in their foraging behavior, expressed as seed collection, under different treatments over time, M. ebeninus was more consistent than M. arenarius. These differences between the species may be expxained by their different colony size, worker size, and range of foraging strategies, among other factors. We suggest that the differences in foraging, such as in food preference and behavioral consistency while foraging, could contribute to the co-occurrence of these 2 species in a similar habitat.

Context-dependent effects of cold stress on behavioral, physiological,and life-history traits of the red flour beetle

Animals are exposed in nature to a variety ofstressors.While stress is generally harmful,mild stress can also be beneficial and contribute to reproduction and survival.We studied the effect of five cold shock events versus a single cold shock and a control group, representing three levels of stress (harsh,mild,and no stress),on behavioral,physiological, and life-history traits of the red flour beetle (Tribolium castaneum,Herbst 1797).Beetles exposed to harsh cold stress were less active than a control group:they moved less and failed more frequently to detect a food patch.Their probability to mate was also lower. Beetle pairs exposed to harsh cold stress frequently failed to reproduce at all,and if reproducing,females laid fewer eggs,which were,as larvae in mid-development,smaller than those in the control group.However,harsh cold stress led to improved female starvation tolerance,probably due to enhanced lipid accumulation.Harsh cold shock also improved tolerance to an additional cold shock compared to the control.Finally,a single cold shock event negatively affected fewer measured response variables than the harsh cold stress, but also enhanced neither starvation tolerance nor tolerance to an additional cold shock. The consequences of a harsher cold stress are thus not solely detrimental but might even enhance survival under stressful conditions.Under benign conditions,nevertheless,harsh stress impedes beetle performance.The harsh stress probably shifted the balance point of the survival-reproduction trade-off,a shift that did not take place following exposure to mild stress.

Wormlions prefer both fine and deep sand but only deep sand leads to better performance

Wormlions are small fly larvae that dig pits in loose soil to trap their prey. Similar to other trapbuilding predators, like spiders and antlions, they depend on the habitat structure for successful trap construction and prey catch. We examined whether sites at which wormlions are present differ in sand depth and particle size from nearby sites, at which wormlions are absent. Next, in the laboratory we manipulated both sand depth and type (fine vs. coarse) to determine their joint effect on microhabitat pref ere nee, the size of the con structed pit, wormlion movement, and their latency to respond to prey. We expected better performance by wormlions in fine and deep sand, and the sand in wormlions' natural sites to be finer and deeper. However, in only partial agreement with our expectations, wormlion sites featured finer sand but not deeper sand. In the laboratory, wormlions preferred both fine and deep sand, and moved more in shallow and coarse sand, which we interpret as an attempt to relocate away from unfavorable conditions. However, only deep sand led to larger pits being constructed and to a faster response to prey. The preference for fine sand could, therefore, be related to other ben efits that sand provides. Fin ally, body mass was a domi nant factor, interacting with the preference for both deep and fine sand: deep over shallow sand was more favored by large wormlions and fine over coarse sand by smaller ones. Our results suggest that several factors should be incorporated when studying microhabitat selection.

Leg or antenna injury in Cataglyphis ants impairs survival but does not hinder searching for food

Injury is common in nature resulting,for example,from fighting,partial predation,or the wear of body parts.Injury is costly,expressed in impaired performance,failure in competition,and a shorter life span.A survey of the literature revealed the frequent occurrence of injury in ants and its various causes.We examined whether leg or antenna injury impacts food-discovery time and reduces the likelihood of reaching food in workers of the desert ant Cataglyphis niger.We examined the search-related consequences of injury in groups of either 4 or 8 workers searching for food in a short arena,a long arena,and a maze.We conducted a small field survey to evaluate the prevalence of injury in the studied population.Finally,we compared the survival rates of injured versus uninjured workers in the laboratory.Injury was common in the field,with almost 9%of the workers collected out of the nest,found to be injured.Injured workers survived shorter than uninjured ones and there was a positive link between injury severity and survival.However,we could not detect an effect of injury on any of the searching-related response variables,neither in the arenas nor in the mazes tested.We suggest that workers that survive such injury are only moderately affected by it.

Evidence for the effect of brief exposure to food,but not learning interference,on maze solving in desert ants

Theories of forgetting highlight 2 active mechanisms through which animals forget prior knowledge by recipro-cal disruption of memories.According to“proactive interference,”information learned previously interferes with the acquisition of new information,whereas“retroactive interference”suggests that newly gathered information interferes with already existing information.Our goal was to examine the possible effect of both mechanisms in the desert ant Cataglyphis niger,which does not use pheromone recruitment,when learning spatial information while searching for food in a maze.Our experiment indicated that neither proactive nor retroactive interference took place in this system although this awaits confirmation with individual-level learning assays.Rather,the ants’persistence or readiness to search for food grew with successive runs in the maze.Elevated persistence led to more ant workers arriving at the food when retested a day later,even if the maze was shifted between runs.We support thisfinding in a second experiment,where ant workers reached the food reward at the maze end in higher numbers after encountering food in the maze entry compared to a treatment,in which food was present only at the maze end.This result suggests that spatial learning and search persistence are 2 parallel behavioral mechanisms,both assisting foraging ants.We suggest that their relative contribution should depend on habitat complexity.