Influence of phylogenetic, environmental, and behavioral factors on the gut bacterial community structure of dung beetles (Scarabaeidae: Scarabaeinae) in a Neotropical Biosphere Reserve.

Gut bacteria help dung beetles metabolize nutrients contained and synthesize those unavailable in their food, depending on the ecological scenario in which they develop. However, less is known about the influence of environmental and behavioral factors on the taxonomic composition of bacterial gut communities in Scarabaeinae beetles. To address this research topic, we analyzed 13 tropical dung beetle species in the Los Tuxtlas Biosphere Reserve, Mexico, to understand how the beetle tribe, habitat, food preference, food relocation, and parental care influence the composition of gut bacterial communities. We found that the beetle tribe is the primary factor impacting the taxonomic composition of gut bacterial communities. Among them, Deltochilini displayed the highest variability in diversity due to the different combinations of habitat and food preferences among its species. On the other hand, the other tribes studied did not exhibit such variable combinations. Habitat emerged as the second most influential factor, with forest-dwelling beetles displaying higher diversity. This can be attributed to the heterogeneous environments within tropical forests, which offer a greater diversity of food resources. In contrast, grassland beetles, living in more homogeneous environments and relying on cow feces as their main food source, exhibited lower diversity. Our findings suggest a correlation between bacterial diversity and food resource availability in complex habitats, such as tropical forests, which offer a wider array of food sources compared to simpler environments like grasslands.

Diversity and Composition of the Gut Microbiota in the Developmental Stages of the Dung Beetle Copris incertus Say (Coleoptera, Scarabaeidae).

Dung beetles are holometabolous insects that feed on herbivorous mammal dung and provide services to the ecosystem including nutrient cycling and soil fertilization. It has been suggested that organisms developing on incomplete diets such as dungs require the association with microorganisms for the synthesis and utilization of nutrients. We describe the diversity and composition of the gut-microbiota during the life cycle of the dung beetle Copris incertus using 16S rRNA gene sequencing. We found that C. incertus gut contained a broad diversity of bacterial groups (1,699 OTUs and 302 genera). The taxonomic composition varied during the beetle life cycle, with the predominance of some bacterial genera in a specific developmental stage (Mothers: Enterobacter and Serratia; Eggs: Nocardioides and Hydrogenophaga; Larval and pupal stages: Dysgonomonas and Parabacteroides; offspring: Ochrobactrum). The beta diversity evidenced similarities among developmental stages, clustering (i) the adult stages (mother, male and female offsprings), (ii) intermediate developmental (larvae and pupa), and (iii) initial stage (egg). Microbiota differences could be attributed to dietary specialization or/and morpho-physiological factors involved in the transition from a developmental stage to the next. The predicted functional profile (PICRUSt2 analysis) for the development bacterial core of the level 3 categories, indicated grouping by developmental stage. Only 36 categories were significant in the SIMPER analysis, including the metabolic categories of amino acids and antibiotic synthesis, which were enriched in the larval and pupal stages; both categories are involved in the metamorphosis process. At the gene level, we found significant differences only in the KOs encoding functions related to nitrogen fixation, uric acid metabolism, and plant cell wall degradation for all developmental stages. Nitrogen fixation and plant cell wall degradation were enriched in the intermediate stages and uric acid metabolism was enriched in mothers. The data reported here suggested the influence of the maternal microbiota in the composition and diversity of the gut microbiota of the offspring.

Ivermectin alters reproductive success, body condition and sexual trait expression in dung beetles.

Ivermectin is a very common parasiticide used in livestock. It is excreted in the dung and has negative effects on survival and reproduction of dung-degrading organisms, including dung beetles. Here we exposed the dung beetle Euoniticellus intermedius to different concentrations of ivermectin in the food and evaluated reproductive success and the expression of traits associated with survival and reproduction under laboratory conditions. It is the first time the effects of ivermectin were evaluated on offspring physiological condition and the expression of a secondary sexual trait. We also registered the number of emerged beetles, sex ratio and body size of emerged adult beetles. Besides reducing the number of emerged beetles and body size, as found in the same and other insects, ivermectin at high doses reduced muscle mass while at intermediate doses it increased lipid mass. Ivermectin changed offspring sex ratio and at high doses increased the size of male horn, which is an important trait defining the male mating success. Our results highlight the importance of regulating parasiticide usage in livestock in order to maintain ecosystem services provided by dung beetles and confirm that contaminants impose new environmental conditions that not only impact on wild animal survival, but also on evolutionary processes such as sexual selection.

Effect of ivermectin on the survival and fecundity of Euoniticellus intermedius (Coleoptera: Scarabaeidae).

The State of Veracruz in Mexico is one of the main cattle producers, and uses several veterinary products for disease and parasite control. For parasite control, ivermectin is one of the most frequently used substances. Nevertheless, even though previous research conducted in other countries has found that this product has negative effects on beneficial coprophagous fauna, no studies have described its effects on coprophagous insects at a local scale in Veracruz, Mexico. This study evaluated Euoniticellus intermedius survival, fecundity, fertility and preimaginal development under laboratory conditions when ivermectin was added to cattle dung at three different concentrations. The design included two controls (spiked dung), and the following product concentrations: 0.01, 1.0 and 100ppm, which were homogenized with wet cattle dung. 20 female-male E. intermedius couples between five and 15 days old were used and kept at 27 degrees C, 70% RH, and 12h light for 10 days. The survival of all specimens, the fertility of 20 females and the gonadal maturity of 17 males were verified. The larval development in 162 pieces of brood-mass was examined, and a total of 974 larvae developed and reached adulthood. The highest ivermectin concentration was toxic at 1.0ppm dose, the survival of adults was reduced to almost the half, and at 100ppm, total mortality was observed. The effects on specimen reproductive systems showed that the ovary was not affected, that the testicle size increased, and that the fecundity and weight of brood-masses were reduced. Pre-imaginal development increased 0.5 times at 0.01ppm concentration, and the width of the cephalic capsule in third instar larvae diminished. The prolonging of development time may cause a phase lag in the field activity cycle, this lag may reduce the number of E. intermedius individuals and the efficiency of the environmental services that they provide.

Effect of ivermectin on the survival and fecundity of Euoniticellus intermedius (Coleoptera: Scarabaeidae)

The State of Veracruz in Mexico is one of the main cattle producers, and uses several veterinary products for disease and parasite control. For parasite control, ivermectin is one of the most frequently used substances. Nevertheless, even though previous research conducted in other countries has found that this product has negative effects on beneficial coprophagous fauna, no studies have descry ibed its effects on coprophagous insects at a local scale in Veracruz, Mexico. This study evaluated Euoniticellus intermedius survival, fecundity, fertility and preimaginal development under laboratory conditions when ivermectin was added to cattle dung at three different concentrations. The design included two controls (spiked dung), and the following product concentrations: 0.01, 1.0 and 100ppm, which were homogenized with wet cattle dung. 20 female-male E. intermedius couples between five and 15 days old were used and kept at 27°C, 70% RH, and 12h light for 10 days. The survival of all specimens, the fertility of 20 females and the gonadal maturity of 17 males were verified. The larval development in 162 pieces of brood-mass was examined, and a total of 974 larvae developed and reached adulthood. The highest ivermectin concentration was toxic at 1.0ppm dose, the survival of adults was reduced to almost the half, and at 100ppm, total mortality was observed. The effects on specimen reproductive systems showed that the ovary was not affected, that the testicle size increased, and that the fecundity and weight of brood-masses were reduced. Pre-imaginal development increased 0.5 times at 0.01ppm concentration, and the width of the cephalic capsule in third instar larvae diminished. The prolonging of development time may cause a phase lag in the field activity cycle, this lag may reduce the number of E. intermedius individuals and the efficiency of the environmental services that they provide.

El estado de Veracruz en México, es uno de los principales productores de ganado vacuno en México, asimismo utiliza diversas medicinas veterinarias para el control de enfermedades y parásitos. La ivermectina es una de las substancias más utilizadas para el control de parásitos. Sin embargo, se sabe por estudios hechos en otros países, que esta substancia tiene efectos negativos sobre la fauna coprófaga benéfica como los escarabajos del estiércol, pero no se han estudiado sus efectos sobre la fauna coprófaga de Veracruz o de México. Este estudio se realizó en condiciones de laboratorio, en donde se utilizó el estiércol vacuno a tres diferentes concentraciones de ivermectina para determinar su efecto sobre la supervivencia, fecundidad, fertilidad y desarrollo preimaginal de Euoniticellus intermedius. Por lo tanto, las tres concentraciones que se emplearon fueron: 0.01, 1.0 y 100ppm de ivermectina homogeneizada en estiércol vacuno fresco y dos testigos. Además, se utilizaron 20 parejas hembramacho por tratamiento, entre cinco y 15 días de edad y mantenidos por 10 días a 27°C, 70% HR y 12hr luz. Se determinó la supervivencia de todos, la fertilidad en 20 hembras y el estado de madurez gonádica en 17 machos. Se determinó el desarrollo preimaginal en 162 masas-nido y 974 se dejaron continuar el desarrollo hasta la emergencia de los adultos. La ivermectina es tóxica a mayor concentración. La supervivencia de adultos se redujo casi a la mitad a dosis de 1.0ppm y fue nula a 100ppm. El ovario no fue afectado. Los testículos incrementaron de tamaño. La fecundidad y el peso de las masas-nido se redujeron. El desarrollo preimaginal se incrementó 0.5 veces a concentración 0.01ppm y las larvas del tercer estadio redujeron el ancho de la cápsula cefálica. El alargamiento del tiempo de desarrollo puede causar desfase de su ciclo de actividad en campo, lo que podría reducir su número y la eficiencia de los servicios ambientales que proporcionan.