The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism

Experimentation is at the heart of classical and modern behavioral ecology research. The manipulation of natural cues allows us to establish causation between aspects of the environment, both internal and external to organisms, and their effects on animals' behaviors. In recognition systems research, including the quest to understand the coevolution of sensory cues and decision rules underlying the rejection of foreign eggs by hosts of avian brood parasites, artificial stimuli have been used extensively, but not without controversy. In response to repeated criticism about the value of artificial stimuli, we describe four potential benefits of using them in egg recognition research, two each at the proximate and ultimate levels of analysis: (1) the standardization of stimuli for developmental studies and (2) the disassociation of correlated traits of egg phenotypes used for sensory discrimination, as well as (3) the estimation of the strength of selection on parasitic egg mimicry and (4) the establishment of the evolved limits of sensory and cognitive plasticity. We also highlight constraints of the artificial stimulus approach and provide a specific test of whether responses to artificial cues can accurately predict responses to natural cues. Artificial stimuli have a general value in ethological research beyond research in brood parasitism and may be especially critical in field studies involving the manipulation of a single parameter, where other, confounding variables are difficult or impossible to control experimentally or statistically.     

Population status and habitat occupancy of endangered river dolphins in the Karnali River system of Nepal during low water season

Ganges river dolphin abundance has undergone a predominant decline across its range since monitoring began. In Nepal, disappearance from some of the rivers it once used has already occurred. Today this species can only be found in three river systems in Nepal, the Karnali, Sapta Koshi, and Narayani, but numbers are low in these locations. To determine the abundance of dolphins remaining in the Karnali system (which includes the Karnali, Geruwa, and Mohana), and factors affecting dolphin habitat use, we conducted surveys where we recorded dolphin presence. Dolphins within this river system were sighted only in the Karnali and an abundance estimate of 5.04 ± 0.753 SE was calculated. This pattern of ranging differed from that previously reported (from previous sightings only in the Geruwa to current sightings only in the Karnali). River depth likely contributed to the presence or absence of dolphins. Shifts in available habitat between the Geruwa and Karnali have resulted from changes in the course of the main stream Karnali following construction of the Chisapani irrigation intake. Because of the low numbers of dolphins reported, there is great concern that loss of this species in Nepal is likely in the near future.     

Lineage‐specific activities of a multipotent mitochondrion of trypanosomatid flagellates

Trypanosomatids are a very diverse group composed of monoxenous and dixenous parasites belonging to the excavate class Kinetoplastea. Here we studied the respiration of five monoxenous species (Blechomonas ayalai, Herpetomonas muscarum, H. samuelpessoai, Leptomonas pyrrhocoris and Sergeia podlipaevi) introduced into culture, each representing a novel yet globally distributed and/or species‐rich clade, and compare them with well‐studied flagellates Trypanosoma brucei, Phytomonas serpens, Crithidia fasciculata and Leishmania tarentolae. Differences in structure and activities of respiratory chain complexes, respiration and other biochemical parameters recorded under laboratory conditions reveal their substantial diversity, likely a reflection of different host environments. Phylogenetic relationships of the analysed trypanosomatids do not correlate with their biochemical parameters, with the differences within clades by far exceeding those among clades. As the S. podlipaevi canonical respiratory chain complexes have very low activities, we believe that its mitochondrion is utilised for purposes other than oxidative phosphorylation. Hence, the single reticulated mitochondrion of diverse trypanosomatids seems to retain multipotency, with the capacity to activate its individual components based on the host environment.     

Behaviour in captivity predicts some aspects of natural behaviour,but not others,in a wild cricket population

Examining the relevance of ‘animal personality’ involves linking consistent among- and within-individual behavioural variation to fitness in the wild. Studies aiming to do this typically assay personality in captivity and rely on the assumption that measures of traits in the laboratory reflect their expression in nature. We examined this rarely tested assumption by comparing laboratory and field measurements of the behaviour of wild field crickets (Gryllus campestris) by continuously monitoring individual behaviour in nature, and repeatedly capturing the same individuals and measuring their behaviour in captivity. We focused on three traits that are frequently examined in personality studies: shyness, activity and exploration. All of them showed repeatability in the laboratory. Laboratory activity and exploration predicted the expression of their equivalent behaviours in the wild, but shyness did not. Traits in the wild were predictably influenced by environmental factors such as temperature and sunlight, but only activity showed appreciable within-individual repeatability. This suggests that some behaviours typically studied as personality traits can be accurately assayed in captivity, but the expression of others may be highly context-specific. Our results highlight the importance of validating the relevance of laboratory behavioural assays to analogous traits measured in the wild.     

New substitution models for rooting phylogenetic trees

The root of a phylogenetic tree is fundamental to its biological interpretation, but standard substitution models do not provide any information on its position. Here, we describe two recently developed models that relax the usual assumptions of stationarity and reversibility, thereby facilitating root inference without the need for an outgroup. We compare the performance of these models on a classic test case for phylogenetic methods, before considering two highly topical questions in evolutionary biology: the deep structure of the tree of life and the root of the archaeal radiation. We show that all three alignments contain meaningful rooting information that can be harnessed by these new models, thus complementing and extending previous work based on outgroup rooting. In particular, our analyses exclude the root of the tree of life from the eukaryotes or Archaea, placing it on the bacterial stem or within the Bacteria. They also exclude the root of the archaeal radiation from several major clades, consistent with analyses using other rooting methods. Overall, our results demonstrate the utility of non-reversible and non-stationary models for rooting phylogenetic trees, and identify areas where further progress can be made.     

CGR2 and CGR3 have critical overlapping roles in pectin methylesterification and plant growth in Arabidopsis thaliana

Pectins are critical polysaccharides of the cell wall that are involved in key aspects of a plant's life, including cell‐wall stiffness, cell‐to‐cell adhesion, and mechanical strength. Pectins undergo methylesterification, which affects their cellular roles. Pectin methyltransferases are believed to methylesterify pectins in the Golgi, but little is known about their identity. To date, there is only circumstantial evidence to support a role for QUASIMODO2 (QUA2)‐like proteins and an unrelated plant‐specific protein, cotton Golgi‐related 3 (CGR3), in pectin methylesterification. To add to the knowledge of pectin biosynthesis, here we characterized a close homolog of CGR3, named CGR2, and evaluated the effect of loss‐of‐function mutants and over‐expression lines of CGR2 and CGR3 in planta. Our results show that, similar to CGR3, CGR2 is a Golgi protein whose enzyme active site is located in the Golgi lumen where pectin methylesterification occurs. Through phenotypical analyses, we also established that simultaneous loss of CGR2 and CGR3 causes severe defects in plant growth and development, supporting critical but overlapping functional roles of these proteins. Qualitative and quantitative cell‐wall analytical assays of the double knockout mutant demonstrated reduced levels of pectin methylesterification, coupled with decreased microsomal pectin methyltransferase activity. Conversely, CGR2 and CGR3 over‐expression lines have markedly opposite phenotypes to the double knockout mutant, with increased cell‐wall methylesterification levels and microsomal pectin methyltransferase activity. Based on these findings, we propose that CGR2 and CGR3 are critical proteins in plant growth and development that act redundantly in pectin methylesterification in the Golgi apparatus.     

Aerobic capacity of Peruvian Quechua: A test of the developmental adaptation hypothesis

High altitude natives are reported to have outstanding work capacity in spite of the challenge of oxygen transport and delivery in hypoxia. To evaluate the developmental effect of lifelong exposure to hypoxia on aerobic capacity, VO_2peak was measured on two groups of Peruvian Quechua subjects (18–35 years), who differed in their developmental exposure to altitude. Male and female volunteers were recruited in Lima, Peru (150 m), and were divided in two groups, based on their developmental exposure to hypoxia, those: a) Born at sea‐level individuals (BSL), with no developmental exposure to hypoxia (n = 34) and b) Born at high‐altitude individuals (BHA) with full developmental exposure to hypoxia (n = 32), but who migrated to sea‐level as adults (>16‐years‐old). Tests were conducted both in normoxia (BP = 750 mm Hg) and normobaric hypoxia at sea‐level (BP = 750 mm Hg, FiO₂ = 0.12, equivalent to 4,449 m), after a 2‐month training period (in order to control for initial differences in physical fitness) at sea‐level. BHA had a significantly higher VO_2peak at hypoxia (40.31 ± 1.0 ml/min/kg) as compared to BSL (35.78 ± 0.96 ml/min/kg, P = 0.001), adjusting for sex. The decrease of VO_2peak at HA relative to SL (ΔVO_2peak) was not different between groups, controlling for baseline levels (VO_2peak at sea‐level) and sex (BHA = 0.35 ± 0.04 l/min, BSL = 0.44 ± 0.04 l/min; P = 0.12). Forced vital capacity (controlling for height) and the residuals of VO_2peak (controlling for weight) had a significant association in the BHA group only (r = 0.155; P = 0.031). In sum, results indicate that developmental exposure to altitude constitutes an important factor to determine superior exercise performance. Am J Phys Anthropol 156:363–373, 2015. © 2014 Wiley Periodicals, Inc.     

Reduced‐risk insecticides in Neotropical stingless bee species: impact on survival and activity

As honeybees are the main pollinator subject to an intense research regarding effects of pesticides, other ecologically important native bee pollinators have received little attention in ecotoxicology and risk assessment of pesticides in general, and insecticides in particular, some of which are perceived as reduced‐risk compounds. Here, the impact of three reduced‐risk insecticides – azadirachtin, spinosad and chlorantraniliprole – was assessed in two species of stingless bees, Partamona helleri and Scaptotrigona xanthotrica, which are important native pollinators in Neotropical America. The neonicotinoid imidacloprid was used as a positive control. Spinosad exhibited high oral and contact toxicities in adult workers of both species at the recommended label rates, with median survival times (LT₅₀s) ranging from 1 to 4 h, whereas these estimates were below 15 min for imidacloprid. Azadirachtin and chlorantraniliprole exhibited low toxicity at the recommended label rates, with negligible mortality that did not allow LT₅₀ estimation. Sublethal behavioural assessments of these two insecticides indicated that neither one of them affected the overall group activity of workers of the two species. However, both azadirachtin and chlorantraniliprole impaired individual flight take‐off of P. helleri and S. xanthotrica worker bees, which may compromise foraging activity, potentially leading to reduced colony survival. These findings challenge the common perception of non‐target safety of reduced‐risk insecticides and bioinsecticides, particularly regarding native pollinator species.