Catherine Numa

Low doses of ivermectin cause sensory and locomotor disorders in dung beetles

Ivermectin is a veterinary pharmaceutical generally used to control the ecto- and endoparasites of livestock, but its use has resulted in adverse effects on coprophilous insects, causing population decline and biodiversity loss. There is currently no information regarding the direct effects of ivermectin on dung beetle physiology and behaviour. Here, based on electroantennography and spontaneous muscle force tests, we show sub-lethal disorders caused by ivermectin in sensory and locomotor systems of Scarabaeus cicatricosus, a key dung beetle species in Mediterranean ecosystems. Our findings show that ivermectin decreases the olfactory and locomotor capacity of dung beetles, preventing them from performing basic biological activities. These effects are observed at concentrations lower than those usually measured in the dung of treated livestock. Taking into account that ivermectin acts on both glutamate-gated and GABA-gated chloride ion channels of nerve and muscle cells, we predict that ivermectin’s effects at the physiological level could influence many members of the dung pat community. The results indicate that the decline of dung beetle populations could be related to the harmful effects of chemical contamination in the dung.

Roles of endothermy in niche differentiation for ball‐rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract 1. An analysis of whether niche differentiation in ball‐rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.

Current protected sites do not allow the representation of endangered invertebrates: the Spanish case

Abstract.  1. Using a recently created database representing the joint effort of around 100 invertebrate taxonomists, this study uses the information on 52 arthropoda and 27 mollusca species that are endangered and critically endangered to examine to what extent invertebrate species are represented in existing Spanish protected areas.

Dung beetles eat acorns to increase their ovarian development and thermal tolerance.

Animals eat different foods in proportions that yield a more favorable balance of nutrients. Despite known examples of these behaviors across different taxa, their ecological and physiological benefits remain unclear. We identified a surprising dietary shift that confers ecophysiological advantages in a dung beetle species. Thorectes lusitanicus, a Mediterranean ecosystem species adapted to eat semi-dry and dry dung (dung-fiber consumers) is also actively attracted to oak acorns, consuming and burying them. Acorn consumption appears to confer potential advantages over beetles that do not eat acorns: acorn-fed beetles showed important improvements in the fat body mass, hemolymph composition, and ovary development. During the reproductive period (October-December) beetles incorporating acorns into their diets should have greatly improved resistance to low-temperature conditions and improved ovarian development. In addition to enhancing the understanding of the relevance of dietary plasticity to the evolutionary biology of dung beetles, these results open the way to a more general understanding of the ecophysiological implications of differential dietary selection on the ecology and biogeography of these insects.

Acorn preference by the dung beetle, Thorectes lusitanicus, under laboratory and field conditions

Processes of seed predation and dispersal are crucial for tree regeneration and forest dynamics. To understand the role of the dung beetle, Thorectes lusitanicus (Col., Scarabaeoidea, Geotrupidae) as secondary seed disperser in Mediterranean oak forests, its food preference was investigated in the field and in the laboratory. This paper had for objectives (1) to explore the feeding preferences for acorns of the two species available in the field: Quercus suber and Quercus canariensis, and (2) to study the olfactory and palatability response of T. lusitanicus to different food resources (oak acorns and dung) under laboratory conditions. The number of beetles in the field was curvilinearly related to the number of acorns, being higher when the number of acorns was intermediate. The maximum values of T. lusitanicus density corresponded to those plots located under Q. suber trees with the highest total weight of acorns. Bioassays with a four-armed olfactometer showed that T. lusitanicus was clearly attracted to volatiles of Q. suber acorns more than to of dung. Palatability bioassays also showed significant preferences for acorns of Q. suber in comparison with the typical food previously described for this beetle species (dung). According to our results, we suggest that a diet based on acorns (due to their high content of polyunsaturated fatty acids) probably satisfies the nutritional requirements of T. lusitanicus during winter, larval development, and metamorphosis.

The Comparative Effectiveness of Rodents and Dung Beetles as Local Seed Dispersers in Mediterranean Oak Forests

The process of seed dispersal of many animal-dispersed plants is frequently mediated by a small set of biotic agents. However, the contribution that each of these dispersers makes to the overall recruitment may differ largely, with important ecological and management implications for the population viability and dynamics of the species implied in these interactions. In this paper, we compared the relative contribution of two local guilds of scatter-hoarding animals with contrasting metabolic requirements and foraging behaviours (rodents and dung beetles) to the overall recruitment of two Quercus species co-occurring in the forests of southern Spain. For this purpose, we considered not only the quantity of dispersed seeds but also the quality of the seed dispersal process. The suitability for recruitment of the microhabitats where the seeds were deposited was evaluated in a multi-stage demographic approach. The highest rates of seed handling and predation occurred in those microhabitats located under shrubs, mostly due to the foraging activity of rodents. However, the probability of a seed being successfully cached was higher in microhabitats located beneath a tree canopy as a result of the feeding behaviour of beetles. Rodents and beetles showed remarkable differences in their effectiveness as local acorn dispersers. Quantitatively, rodents were much more important than beetles because they dispersed the vast majority of acorns. However, they were qualitatively less effective because they consumed a high proportion of them (over 95%), and seeds were mostly dispersed under shrubs, a less suitable microhabitat for short-term recruitment of the two oak species. Our findings demonstrate that certain species of dung beetles (such as Thorectes lusitanicus), despite being quantitatively less important than rodents, can act as effective local seed dispersers of Mediterranean oak species. Changes in the abundance of beetle populations could thus have profound implications for oak recruitment and community dynamics.

Comparing Dung Beetle Species Assemblages Between Protected Areas and Adjacent Pasturelands in a Mediterranean Savanna Landscape

Abstract Dung beetles are considered keystone species because of their role in decomposition, seed dispersal, and control of vertebrate parasites in grazed habitats. Despite the ecological importance of this group to pasture ecosystem functioning, still little is known about its relationship with grazing management activities. We evaluated the conservation value of protected areas for dung beetle diversity by comparing two different management conditions of Mediterranean savanna in central Spain. Four different sites with wild herbivory (red deer, roe deer) were sampled inside the Cabañeros National Park, and four sites with traditional agrosilvopastoral management were sampled in a sheep farm near the park. The dung beetle species richness was similar between savanna conditions, but the total dung beetle abundance and biomass were considerably greater in the park grasslands than in the grasslands of the sheep farm. Dung beetle species composition, species dominance, and abundance by functional groups from both park and farm sites were different, despite the high similarity among the sampled sites in both hydric content and dung availability. Onthophagus maki (Illiger 1803) and O. furcatus (Fabricius 1781) were the dominant species in the park, while O. furcatus, Aphodius foetidus (Herbst 1783), and Caccobius schreberi L. were the dominant species on the farm. Species richness and abundance of telecoprids were higher in the park than on the farm. Abundance of paracoprids was also higher in the park than on the farm, while no differences in species richness and abundance of endocoprids were observed between both conditions. These results suggest that management activities such as plowing and the use of veterinary substances affect soil structure and dung quality and could be important factors that alter dung beetle assemblages in terms of composition, abundance, and biomass on traditional farms.

Spatiotemporal Variation of Scarab Beetle Assemblages (Coleoptera: Scarabaeidae: Dynastinae, Melolonthinae, Rutelinae) in the Premontane Rain Forest in Costa Rica: A Question of Scale

ABSTRACT Biodiversity of tropical forests varies at spatial and temporal scales, but at what scale and how the assemblages differ when we consider the same kind of forest and the same altitude has been poorly documented. We examined the variation in species richness and composition of three subfamilies of scarab beetles (Dynastinae, Rutelinae, and Melolonthinae) along a northwest-southeast (NW-SE) transect of premontane rain forests in Costa Rica. Sampling was carried out at six sampling sites comprising three mountain ranges. Two forest sites were selected in each mountain range at the same altitudinal strip and same life zone. We conducted eight field surveys from June 2007 to January 2008. UV light traps were used to catch the beetles. We studied beetle diversity at three spatiotemporal levels: mountain range, forest site, and monthly trap. Species composition and richness varied at the three levels studied, and this variation was not necessarily related with geographic distance. Forest site and monthly trap levels showed higher variation in similarity indices than the mountain range level did. Additive partitioning of diversity showed values of diversity higher than expected only at the spatial levels with the mountain ranges showing the highest contribution to gamma diversity. Our results show high spatiotemporal variation in scarab beetle assemblages across Costa Rican premontane rain forests and underline that the analysis of a variety of spatiotemporal scales within a single kind of forest is crucial to understand scarab beetle biodiversity patterns in forest ecosystems.

Scaling local abundance determinants in mediterranean dung beetles

Abstract.  1. We study the factors that contribute to the variation in the local abundance of dung beetle species inhabiting Cabañeros National Park, a Mediterranean reserve in Central Spain. The relative roles of five different groups of explanatory variables (climatic, local‐scale vegetation, landscape‐scale vegetation, landscape connectivity and trophic resources) were assessed for 27 sampling sites established by a nested hierarchical sampling design that considered three regional landscapes (woodland, scrubland, grassland) and three local habitat types (forest, scrub, pasture) within each landscape.

Ivermectin residues disrupt dung beetle diversity, soil properties and ecosystem functioning: An interdisciplinary field study

Ivermectin is the most common endectocide used to control parasites affecting livestock. Short-term physiological and behavioural effects of ivermectin on dung beetles may have long-term consequences for beetle populations and ecosystem functioning. Long-term effects of the use of ivermectin can be estimated by comparing dung assemblages and ecosystem functions in areas with conventional ivermectin-treated livestock and environmentally similar areas in which livestock are not treated with veterinary medical products (organic farming). In this study, we investigated both short-term and long-term effects of the administration of ivermectin on the characteristics of dung beetle assemblages and the services they provided in a protected area (Doñana National Park, SW Spain). We examined short-term dung colonization, dwelling, relocation, and disaggregation rates and the associations between these processes and the key assemblage parameters of species richness, abundance, biomass and functional diversity. Furthermore, we analysed changes in soil physical-chemical properties and processes. Short-term differences were observed in the total amount of dung relocated by dung beetles at different colonization vs. emigration stages, suggesting that dung beetles in this area were affected by the recent treatments of livestock with ivermectin. Moreover, short-term effects could also be responsible for the significant differences in dung spreading rates between sites. Conventional use of ivermectin disrupted ecosystem functioning by affecting species richness, abundance and biomass. The decrease in diversity parameters was related to a reduction in the functional efficiency, which resulted in the long-term accumulation of dung on the ground and considerable changes in soil functionality.