Shai Markman

Predator‐released hydrocarbons repel oviposition by a mosquito

Prey species commonly use predator-released kairomones (PRKs) to detect risk of predation, yet the chemical identity of PRKs remains elusive. Chemical identification of PRKs will facilitate the study of predator-prey interactions and the risk of predation, and when the prey are pests, will potentially provide environmentally friendly means of pest control. In temporary pools of the Mediterranean and Middle East, larvae of the mosquito Culiseta longiareolata Macquart are highly vulnerable to the common predatory backswimmer, Notonecta maculata Fabricius. We demonstrate that N. maculata releases two hydrocarbons, n-heneicosane and n-tricosane, which repel ovipositing females of C. longiareolata. In behavioural tests with environmentally relevant chemical concentrations in outdoor mesocosm experiments, the repellent effects of the two compounds were additive at the tested concentrations.

Detection of endocrine disrupting chemicals in aerial invertebrates at sewage treatment works

Endocrine disrupting chemicals (EDCs) constitute a diverse group of chemical compounds which can alter endocrine function in exposed animals. Whilst most studies have focussed on exposure of wildlife to EDCs via aquatic routes, there is the potential for transfer into the terrestrial food chain through consumption of contaminated prey items developing in sewage sludge and waste water at sewage treatment works. In this study, we determine levels of EDCs in aerial insects whose larval stages develop on percolating filter beds at sewage treatment works. We compare absolute concentrations of known EDCs with those collected from aquatic environments not exposed to sewage effluent outflow. Our findings document for the first time that aerial invertebrates developing on sewage filter beds take up a range of chemicals thought to be incorporated from the sewage effluent, which act as endocrine disruptors. For two synthetic chemicals (17alpha-ethinylestradiol and butylated hydroxy aniline), concentrations were significantly higher in insects captured around percolating filter beds than sites over 2 km from the nearest sewage works. A number of species of insectivorous bats and birds, some of which are declining or threatened, use sewage works as principle foraging sites. We calculate approximate exposure levels for a species of bat known to forage within sewage works and suggest that further research is warranted to assess the ecological implications of consuming contaminated invertebrate prey.

Oviposition habitat selection by Anopheles gambiae in response to chemical cues by Notonecta maculata

ABSTRACT: A number of mosquito species avoid predator-inhabited oviposition sites by detecting predator-released kairomones. In the laboratory, we found that when offered de-ionized water and de-ionized water conditioned with Notonecta maculata, gravid Anopheles gambiae females preferentially oviposited into the former. We then conducted further experiments using two chemical components found in Notonecta-conditioned water, chemically pure n-tricosane and/or n-heneicosane, that was previously shown to repel oviposition by Culiseta longiareolata. These hydrocarbons failed to deter oviposition by An. gambiae females. Thus, different mosquito species may rely on distinct chemical cues to avoid predators. Identification and chemical characterization of such kairomones could facilitate innovative, environmentally sound mosquito control.

Immediate Effects of Nectar Robbing by Palestine Sunbirds (Nectarinia osea) on Nectar Alkaloid Concentrations in Tree Tobacco (Nicotiana glauca)

Plant secondary metabolites (PSMs), such as alkaloids, are often found in many parts of a plant, including flowers, providing protection to the plant from various types of herbivores or microbes. PSMs are also present in the floral nectar of many species, but typically at lower concentrations than in other parts of the plant. Nectar robbers often damage floral tissue to access the nectar. By doing so, these nectar robbers may initiate an increase of PSMs in the floral nectar. It is often assumed that it takes at least a few hours before the plant demonstrates an increase in PSMs. Here, we addressed the question of whether PSMs in the floral tissue are immediately being released into the floral nectar following nectar robbing. To address this research question, we investigated whether there was an immediate effect of nectar robbing by the Palestine Sunbird (Nectarinia osea) on the concentration of nectar alkaloids, nicotine and anabasine, in Tree Tobacco (Nicotiana glauca). We found that the concentration of anabasine, but not nicotine, significantly increased in floral nectar immediately following simulated nectar robbing. These findings suggest that nectar robbers could be ingesting greater amounts of PSMs than they would if they visit flowers legitimately. As a consequence, increased consumption of neurotoxic nectar alkaloids or other PSMs could have negative effects on the nectar robber.

Differential aggressiveness between fire salamander (Salamandra infraimmaculata) larvae covaries with their genetic similarity

Responding differentially to kin and non-kin is known to be adaptive in many species. One example is the inclusive fitness benefits of reducing aggression toward closer relatives. Little is known, however, about the ability of animals to assess differential degrees of genetic relatedness and to respond accordingly with differential levels of aggression. In the present study, we tested whether aggressiveness between body mass-matched pairs of fire salamander (Salamandra infraimmaculata) larvae covaried with the genetic similarity between them. We quantified aggressiveness at three levels of genetic similarity by selecting pairs within and across pools from recently genotyped populations. We also assessed aggression between pairs of siblings. Aggression and associated injuries decreased as genetic similarity increased across the groups. These findings suggest that cannibalistic salamanders can assess their degree of genetic relatedness to conspecifics and vary their behavioral responses depending on the degree of similarity between them along a genetic relatedness continuum.

Climate change and coevolution in the cuckoo-reed warbler system

The evolution of traits in hosts may be influenced by their parasites and vice versa and a coevolutionary arms race often develops between the two. As part of such an arms race, the common cuckoo mimics the eggs of its hosts to avoid egg rejection. Traits related to this arms race may also be influenced by climatic conditions, such as temperature, affecting, for example, food availability and, thus, female condition and egg size (therefore may reflect Bergmann’s rule or the resource rule). The potential interaction between coevolution and climate has rarely been studied. We investigated whether egg and body size of cuckoos and reed warblers from Britain and Denmark had undergone change between 1868 and 1956, and whether such changes were correlated with climatic factors. Cuckoo egg size decreased during the studied period while warbler egg size remained stable. Hence, cuckoo and warbler eggs have become more similar in size over time. Cuckoo egg volume decreased with increasing annual precipitation, but annual precipitation decreased over time. Warbler egg volume increased with spring temperatures (which could not reflect Bergmann’s rule, but may support the resource rule). Hence, it seems that the measured climatic indices did not affect cuckoo egg size but may in part affect warbler egg size. Therefore, the decrease in cuckoo egg size may be the result of the coevolutionary arms race. Body and egg sizes in the cuckoos were negatively correlated whereas warbler body and egg sizes were uncorrelated, suggesting that selection probably acted on egg size directly and not via selection on body size. Taken together, these findings may indicate that climate change, the coevolutionary arms race, or both, affected egg sizes. It is suggested that drawing conclusions regarding the arms race without taking into account other selective pressures (e.g., climate) may confound conclusions regarding parasite-host systems.

Parental self-feeding effects on parental care levels and time allocation in Palestine sunbirds.

The trade-off between parents feeding themselves and their young is an important life history problem that can be considered in terms of optimal behavioral strategies. Recent studies on birds have tested how parents allocate the food between themselves and their young. Until now the effect of food consumption by parent birds on their food delivery to their young as well as other parental activities has rarely been studied. I have previously shown that parent Palestine sunbirds (Nectarinia osea) will consume nectar and liquidized arthropods from artificial feeders. However, they will only feed their young with whole arthropods. This provided a unique opportunity to experimentally manipulate the food eaten by parents independent of that fed to their offspring. Here, I hypothesized that parents invest in their current young according to the quality of food that they themselves consume. Breeding pairs with two or three nestlings were provided with feeders containing water (control), sucrose solution (0.75 mol) or liquidized mealworms mixed with sucrose solution (0.75 mol). As food quality in feeders increased (from water up to liquidized mealworms mixed with sucrose solution): 1) Parents (especially females) increased their food delivery of whole arthropod prey to their young. 2) Only males increased their nest guarding effort. Nestling food intake and growth rate increased with increasing food quality of parents and decreasing brood size. These results imply that increasing the nutrient content of foods consumed by parent sunbirds allow them to increase the rate at which other foods are delivered to their young and to increase the time spent on other parental care activities.

The effect of intruders on territorial Palestine Sunbirds (Nectarinia osea) during the pre-egg laying period

AbstractIn monogamous species, conspecific aggression is a primary tactic to deter intruders. Alternative reproductive strategies, such as extra-pair copulations or intra-specific brood parasitism that peak at the pre-egg laying period and are practised by intruders, pose a significant threat to the monogamous pair. Here, we addressed the question whether male and female Palestine Sunbirds (Nectarinia osea) demonstrate different aggression levels toward conspecific intruders during the pre-egg laying period. We further asked whether indirect measures of certainty of paternity affect male aggression toward such intruders. For that, we measured the aggression of both partners toward intruders while using stuffed birds. We conducted two experiments on a monogamous and territorial Palestine Sunbird population. In the first experiment, we exposed breeding pairs to a conspecific or a heterospecific intruder and measured their aggression toward it. During the second experiment, we exposed breeding pairs to an intruder, before and after temporarily removing the local male. The local male demonstrated higher aggression than the local female toward a male decoy. Toward a female decoy, the local male demonstrated lower aggression than the local female. Following their release, the removed males did not change their aggression toward the male decoy, but rather they decreased their aggression toward the female decoy. These results suggest that the indirect male’s certainty of paternity may be an important factor of the male’s interests when he faces a risk of potential intra-specific brood parasitism. Furthermore, these findings suggest that each gender is more sensitive to its similar intruder gender, and acts according to its interests in terms of its aggression toward the intruder.ZusammenfassungDie Wirkung von Eindringlingen auf territoriale Jerichonektarvögel (Nectarinia osea) vor der Eiablage Bei monogam lebenden Vögeln ist Aggression unter Artgenossen eine primäre Taktik, um Eindringlinge abzuwehren. Alternative reproduktive Strategien, wie zusätzliche Kopulationen oder intra-spezifischer Brutparasitismus, die vor allem vor der Eiablage durch Konkurrenten praktiziert werden, stellen eine erhebliche Bedrohung für den Bruterfolg des monogamen Paares dar. In diesem Kontext stellten wir die Frage, ob männliche und weibliche Jerichonektarvögel (Nectarinia osea) verschieden hohe Aggressionslevel gegenüber eindringenden Artgenossen vor der Eiablage zeigen. Weiterhin fragten wir uns, ob eine indirekte Abschätzung der Gefahr einer Fremdvaterschaft durch die Männchen deren Aggression gegen solche Eindringlinge beeinflusst. Dafür haben wir den Aggressionslevel der beiden Partner auf Eindringlinge mit Hilfe präparierter Vögel beobachtet. Es wurden zwei Experimente an einer monogamen, territorialen Jerichonektarvogel-Population durchgeführt. Im ersten Experiment konfrontierten wir Brutpaare mit einem Artgenossen oder artfremden Eindringling und bestimmten ihre Aggression gegen ihn. Im zweiten Experiment setzten wir den Brutpaaren einen Eindringling vor, wobei das Männchen des Paares temporär entfernt und wieder dazu gesetzt und die Aggressionen beider Partner bestimmt wurde. Die Männchen der untersuchten Paare demonstrierten eine höhere Aggression als die weiblichen Partner gegenüber einem männlichen Lockvogel. Gegen einen weiblichen Lockvogel verhielten sich die Männchen allerdings weniger aggressiv als die Weiblichen. Nachdem die entfernten Männchen dem Versuch wieder zugefügt wurden, hatte sich ihre Aggression gegenüber dem männlichen Eindringling nicht geändert, dem weiblichen Lockvogel gegenüber waren sie aber noch weniger aggressiv. Diese Ergebnisse legen nahe, dass das Risiko einer Fremdvaterschaft eine wichtige Triebkraft im Verhalten der Männchen ist, wenn sie der Gefahr eines möglichen intra-spezifischen Brutparasitismus gegenüber stehen. Darüber hinaus zeigen unsere Ergebnisse, dass jedes Geschlecht sensibler auf Eindringling desselben Geschlechts reagiert, und sich entsprechend seiner Interessen in Bezug auf seine Aggression gegen Eindringlinge verhält.

February precipitation in the wintering grounds of the lesser whitethroat, Sylvia curruca: is it a cue for migration onset?

Numerous studies report shifts in bird migration phenology, presumably owing to global warming. However, most studies focus on migration patterns in the Northern Hemisphere. In this study, we investigated associations between weather conditions in African wintering grounds of the lesser whitethroat, Sylvia curruca, and spring arrival time in Eilat, Israel. Using multivariate regression models, we analysed a 30-year dataset in order to examine correlations between median springtime arrival and 46 climate variables of the wintering quarters. The model obtained exhibited a highly statistical fit, involving mean precipitation in February and March with negative effects and number of wet days during November–February. February precipitation levels were also the major factor associated with the interquartile range of arrival time. Interestingly and contrary to published results, annual or seasonal precipitation showed no correlation with spring arrival time, nor did temperature. Moreover, winter in this region falls into dry season with negligible rainfall quantities. Hence, it is unlikely that precipitation effect on habitat productivity is a driving force of migration, as suggested by other studies. Instead, we propose that precipitation in February acts as a cue for the birds, indicating the approach of spring and migration time.

Nectar alkaloids of tree tobacco can reduce Palestine sunbird foraging performance in a colour discrimination task

Many plant species contain plant secondary metabolites (PSMs), such as alkaloids, in their tissues for protection against herbivore attack, but PSMs can also be found in floral nectar. Some pollinators have been shown to discriminate against floral nectar with PSMs and consuming PSMs may have negative fitness effects on pollinators. However, only a few studies have investigated the effects of ecologically relevant levels of PSMs on pollinator foraging performance. Here, we addressed the question of whether the natural concentrations of the alkaloids, nicotine and anabasine, found in tree tobacco, Nicotiana glauca, nectar affect foraging performance in Palestine sunbird, Nectarinia osea, pollinators that use the plants nectar as a food source. We trained foraging sunbirds to discriminate between rewarding and nonrewarding artificial flowers based on colour. We measured sunbird foraging performance through their accuracy at distinguishing the two colours immediately after training (pretreatment), and again the following day after consuming sucrose solutions with or without alkaloids (post-treatment). We also explored other potential effects of PSM consumption by assessing bird activity level and flower visit rate. Birds that consumed alkaloids did not significantly change their activity level or flower visit rate across time (pre- and post-treatment) compared to birds that did not consume alkaloids (no significant time by treatment interaction). However, alkaloid consumption significantly decreased sunbird foraging performance in terms of their accuracy in distinguishing the rewarding colour, potentially due to reduced memory retention and/or other cognitive or physiological impairments following alkaloid consumption. We also found that sunbirds discriminated against higher, in favour of lower, ecologically relevant alkaloid concentrations in the nectar of tree tobacco and that previous exposure to alkaloids reduced overall consumption of alkaloid solutions. Reduced foraging performance due to PSM ingestion could greatly affect a pollinators foraging efficiency, which could, in turn, affect both pollinator and plant reproductive fitness.