Back to the light, coevolution between vision and olfaction in the "Dark-flies" (Drosophila melanogaster)

Preoperative intravenous mannitol administration and its rationale before cataract surgery

BACKGROUND

The purpose of this study is to assess the variations in anterior chamber depth (ACD), axial length (AXL), and intraocular pressure (IOP) in both phakic and pseudophakic eyes undergoing preoperative intravenous mannitol infusion. The study was conducted at the Ophthalmology Department of IRCSS Humanitas in Milan, Italy. This is a prospective and non-randomized study.

METHODS

40 patients with phakic eyes and 40 patients with pseudophakic eyes scheduled for cataract surgery in their fellow eye were included. Prior to the surgery, comprehensive ophthalmic examinations were conducted, including IOP measurement, and bilateral biometry performed with Anterion® (Heidelberg Engineering GmbH, 69,115, Heidelberg, Germany). All patients received intravenous infusion of mannitol before the surgery. One hour after cataract extraction, the patients underwent the same set of examinations. We analyzed the changes AXL, ACD and IOP in the eye opposite to the one that underwent surgery.

RESULTS

The comparison between preoperative and postoperative parameters showed no differences in AXL (p = 0.34 and p = 0.53) and in ACD (p = 0.38 and p = 0.31) in the phakic and in the pseudophakic group, respectively. Instead, a statistically significant difference was found between the mean preoperative and postoperative IOP (p = 0.02) for the phakic group and (p = 0.03) for the pseudophakic group.

CONCLUSIONS

The administration of mannitol does not lead to any changes in the ACD and AXL, regardless of whether the eyes are phakic or pseudophakic. However, there is a statistically significant reduction in IOP. Nonetheless, it is important to consider the various side effects associated with mannitol infusion.

Evolution of compound eye morphology underlies differences in vision between closely related Drosophila species

BACKGROUND

Insects have evolved complex visual systems and display an astonishing range of adaptations for diverse ecological niches. Species of Drosophila melanogaster subgroup exhibit extensive intra- and interspecific differences in compound eye size. These differences provide an excellent opportunity to better understand variation in insect eye structure and the impact on vision. Here we further explored the difference in eye size between D. mauritiana and its sibling species D. simulans.

RESULTS

We confirmed that D. mauritiana have rapidly evolved larger eyes as a result of more and wider ommatidia than D. simulans since they recently diverged approximately 240,000 years ago. The functional impact of eye size, and specifically ommatidia size, is often only estimated based on the rigid surface morphology of the compound eye. Therefore, we used 3D synchrotron radiation tomography to measure optical parameters in 3D, predict optical capacity, and compare the modelled vision to in vivo optomotor responses. Our optical models predicted higher contrast sensitivity for D. mauritiana, which we verified by presenting sinusoidal gratings to tethered flies in a flight arena. Similarly, we confirmed the higher spatial acuity predicted for Drosophila simulans with smaller ommatidia and found evidence for higher temporal resolution.

CONCLUSIONS

Our study demonstrates that even subtle differences in ommatidia size between closely related Drosophila species can impact the vision of these insects. Therefore, further comparative studies of intra- and interspecific variation in eye morphology and the consequences for vision among other Drosophila species, other dipterans and other insects are needed to better understand compound eye structure-function and how the diversification of eye size, shape, and function has helped insects to adapt to the vast range of ecological niches.

Genomic insight into the nocturnal adaptation of the black-crowned night heron (Nycticorax nycticorax)

BACKGROUND

The black-crowned night heron (Nycticorax nycticorax) is an ardeid bird successfully adapted to the nocturnal environment. Previous studies had indicated that the eyes of the night herons have evolved several specialized morphological traits favoring nocturnal vision. However, the molecular mechanisms of the nocturnal vision adaptation of night herons remained inattentions. In this study, the whole genome of N. nycticorax was sequenced and comparative analyses were performed on the vision-related and olfactory receptor (OR) genes to understand the molecular mechanisms of the visual and olfactory adaptation of night herons.

RESULTS

The results indicated that a number of vision genes were under positive or relaxed selection in N. nycticorax, whereas a number of other vision genes were under relaxed or intensified selection in the boat-billed heron (Cochlearius cochlearius), which suggested that the two species adapt to nocturnality with different genetic mechanisms. The different selections acting on vision genes are probably associated with the enlargement of eye size and the enhancement of visual sensitivity in night herons. The analyses on olfactory receptor (OR) genes indicated that the total number of OR genes in the genomes of N. nycticorax and C. cochlearius were about half those in the little egret (Egretta garzetta), whereas the diversity of their OR genes was not remarkably different. Additionally, the number of expressed OR genes in the transcriptomes of N. nycticorax was also fewer than that in E. garzetta. These results suggest a reduced olfactory capability in night herons compared with E. garzetta.

CONCLUSIONS

Our results provided evidence that several vision genes of the night herons were subjected to different natural selections, which can contribute to a better understanding of the genetic mechanisms of visual adaptions of the night heron. In addition, the finding of the reduced number of total and expressed OR genes in night herons may reflect a trade-off between olfaction and vision.

A Dual Role for Behavior in Evolution and Shaping Organismal Selective Environments

The hypothesis that evolved behaviors play a determining role in facilitating and impeding the evolution of other traits has been discussed for more than 100 years with little consensus beyond an agreement that the ideas are theoretically plausible in accord with the Modern Synthesis. Many recent reviews of the genomic, epigenetic, and developmental mechanisms underpinning major behavioral transitions show how facultative expression of novel behaviors can lead to the evolution of obligate behaviors and structures that enhance behavioral function. Phylogenetic and genomic studies indicate that behavioral traits are generally evolutionarily more labile than other traits and that they help shape selective environments on the latter traits. Adaptive decision-making to encounter resources and avoid stress sources requires specific sensory inputs, which behaviorally shape selective environments by determining those features of the external world that are biologically relevant. These recent findings support the hypothesis of a dual role for behavior in evolution and are consistent with current evolutionary theory.

Neuroanatomical differentiation associated with alternative reproductive tactics in male arid land bees, Centris pallida and Amegilla dawsoni

Alternative reproductive tactics (ARTs) occur when there is categorical variation in the reproductive strategies of a sex within a population. These different behavioral phenotypes can expose animals to distinct cognitive challenges, which may be addressed through neuroanatomical differentiation. The dramatic phenotypic plasticity underlying ARTs provides a powerful opportunity to study how intraspecific nervous system variation can support distinct cognitive abilities. We hypothesized that conspecific animals pursuing ARTs would exhibit dissimilar brain architecture. Dimorphic males of the bee species Centris pallida and Amegilla dawsoni use alternative mate location strategies that rely primarily on either olfaction (large-morph) or vision (small-morph) to find females. This variation in behavior led us to predict increased volumes of the brain regions supporting their primarily chemosensory or visual mate location strategies. Large-morph males relying mainly on olfaction had relatively larger antennal lobes and relatively smaller optic lobes than small-morph males relying primarily on visual cues. In both species, as relative volumes of the optic lobe increased, the relative volume of the antennal lobe decreased. In addition, A. dawsoni large males had relatively larger mushroom body lips, which process olfactory inputs. Our results suggest that the divergent behavioral strategies in ART systems can be associated with neuroanatomical differentiation.

A Review of Effects of Environment on Brain Size in Insects

Simple Summary

What makes a big brain is fascinating since it is considered as a measure of intelligence. Above all, brain size is associated with body size. If species that have evolved with complex social behaviours possess relatively bigger brains than those deprived of such behaviours, this does not constitute the only factor affecting brain size. Other factors such as individual experience or surrounding environment also play roles in the size of the brain. In this review, I summarize the recent findings about the effects of environment on brain size in insects. I also discuss evidence about how the environment has an impact on sensory systems and influences brain size.

Abstract

Brain size fascinates society as well as researchers since it is a measure often associated with intelligence and was used to define species with high “intellectual capabilities”. In general, brain size is correlated with body size. However, there are disparities in terms of relative brain size between species that may be explained by several factors such as the complexity of social behaviour, the ‘social brain hypothesis’, or learning and memory capabilities. These disparities are used to classify species according to an ‘encephalization quotient’. However, environment also has an important role on the development and evolution of brain size. In this review, I summarise the recent studies looking at the effects of environment on brain size in insects, and introduce the idea that the role of environment might be mediated through the relationship between olfaction and vision. I also discussed this idea with studies that contradict this way of thinking.

Multiple loci linked to inversions are associated with eye size variation in species of the Drosophila virilis phylad

The size and shape of organs is tightly controlled to achieve optimal function. Natural morphological variations often represent functional adaptations to an ever-changing environment. For instance, variation in head morphology is pervasive in insects and the underlying molecular basis is starting to be revealed in the Drosophila genus for species of the melanogaster group. However, it remains unclear whether similar diversifications are governed by similar or different molecular mechanisms over longer timescales. To address this issue, we used species of the virilis phylad because they have been diverging from D. melanogaster for at least 40 million years. Our comprehensive morphological survey revealed remarkable differences in eye size and head shape among these species with D. novamexicana having the smallest eyes and southern D. americana populations having the largest eyes. We show that the genetic architecture underlying eye size variation is complex with multiple associated genetic variants located on most chromosomes. Our genome wide association study (GWAS) strongly suggests that some of the putative causative variants are associated with the presence of inversions. Indeed, northern populations of D. americana share derived inversions with D. novamexicana and they show smaller eyes compared to southern ones. Intriguingly, we observed a significant enrichment of genes involved in eye development on the 4th chromosome after intersecting chromosomal regions associated with phenotypic differences with those showing high differentiation among D. americana populations. We propose that variants associated with chromosomal inversions contribute to both intra- and interspecific variation in eye size among species of the virilis phylad.

Divergent sensory investment mirrors potential speciation via niche partitioning across Drosophila

The examination of phylogenetic and phenotypic characteristics of the nervous system, such as behavior and neuroanatomy, can be utilized as a means to assess speciation. Recent studies have proposed a fundamental tradeoff between two sensory organs, the eye and the antenna. However, the identification of ecological mechanisms for this observed tradeoff have not been firmly established. Our current study examines several monophyletic species within the obscura group, and asserts that despite their close relatedness and overlapping ecology, they deviate strongly in both visual and olfactory investment. We contend that both courtship and microhabitat preferences support the observed inverse variation in these sensory traits. Here, this variation in visual and olfactory investment seems to provide relaxed competition, a process by which similar species can use a shared environment differently and in ways that help them coexist. Moreover, that behavioral separation according to light gradients occurs first, and subsequently, courtship deviations arise.