Biology subjects

Tully, T.

Publications and source records attributed to Tully, T..

6 recordsLinked to original sources

bioRxiv2025

Diversity and Community Structure of Collembola (Hexapoda) across sites and microhabitats in the Bula Protected Area, a UNESCO-Listed Hyrcanian Forest at the Crossroads of Two Biodiversity Hotspots (Iran).

Background. The Hyrcanian Forests of Iran, a unique 850 km stretch of deciduous forest along the southern coast of the Caspian Sea, are renowned for their exceptional biodiversity, high levels of endemism and ecological integrity. The northern part of this forest massif is part of the Caucasian Biodiversity Hotspot, while its southern fringe extends into the Iranian-Anatolian Hotspot. The recognition of these forests as a UNESCO World Heritage Site has focused global attention on their protection, primarily from human disturbance. While the diversity of vascular plants is well documented, other groups, such as soil-dwelling arthropods, remain under-explored. This study aims to fill this knowledge gap by conducting inventories in different sections of the Bula Forest, located in the eastern part of the Hyrcanian region, with a focus on Collembola, a potentially diverse but understudied group of soil fauna. The study was conducted to answer the following questions: Is the naturalness and degree of conservation of these forests reflected in the biodiversity of springtail communities? To what extent does the composition and diversity of these communities vary between different sites and microhabitats within these forests? Methods. To answer these questions, 89 samples were collected over a two-year period from three different forest sites that had undergone contrasting forest management. Specifically, the study focused on three forest ecosystems, a preserved anthropized (planted) forest (PAF), a preserved natural forest (PNF) and a non-preserved natural forest (NPF), all located in the Bula protected area. Three types of microhabitats were sampled at each site, including moss, litter and soil, and dead wood. The springtails collected were identified and counted (approximately 3,000 individuals in total), allowing various biodiversity indices to be calculated for the communities as a whole, as well as by site and microhabitat. Soil samples were also analysed to compare soil properties between the three sites. Results. The results reveal an impressive diversity of springtails, with 73 morphospecies identified, belonging to 39 genera and 12 families. Of these, 49 could be identified to species level. The estimated total species richness (gamma) ranged from 80 to 110 species. The analyses also revealed differences in species richness between sites, with two preserved sites (PAF and PNF) having a greater number of species compared to the non-preserved site (NPF), and in microhabitats, with greater diversity observed in dead wood, followed by soil and then mosses. A more detailed analysis of the communities showed a high degree of interspecific diversity in terms of abundance and distribution, without revealing strong patterns of ecological specialization for the majority of species. An analysis of co-occurrences showed that, in most cases species interactions appeared to be neutral. However, some pairs of species showed positive associations, while negative interactions were more marginal. Discussion. The Bula Forest host particularly diverse Collembola communities. The results underline the importance of conserving these environments, which harbours a high diversity of springtails. Additionally, the results highlight the crucial role of dead wood as a substrate in supporting this biodiversity. The results also call for a more in-depth investigation of the factors influencing the presence, absence and abundance of species, as well as an exploration of the underlying causes of positive or negative species covariation.

ecology↗

bioRxiv2024

Effects of environmental and individual variation on time patterns of extinction in small experimental populations.

Predicting the fate of small populations is essential in ecology, epidemiology and conservation biology. Small populations can go extinct quickly or can develop into large established populations. These can still go extinct through demographic stochasticity, especially when declines in mean population size or large size fluctuations drive them into an extinction vortex. Individual life stage and environmental conditions experienced by founding individuals are two factors expected to determine the fate of small populations. When they dont go extinct, life stage effects are expected to wash out. Initial environmental differences equally so, unless differences in environmental conditions continue to occur. We used the parthenogenetic Collembola Folsomia candida to investigate such effects in a crossed treatment on 290 replicate populations, each initiated with a single individual. Populations were initiated with founders of three different life stages and subjected to four levels of culling. Their extinction times were recorded in a period of up to 41 weeks after initiation. We fitted the parameters of an age-structured multi-type branching process model to extinction rates observed in the first weeks after initiation. As predicted by the model, extinction probabilities early in the experiment increased with the level of culling. Extinction probabilities were larger in populations founded by non-reproducing individuals. These decreased over time, presumably because of the onset of reproduction. In established populations, extinction probabilities increased with culling level and the effects of the founder stage disappeared, except for a late increase in extinction probability in populations founded by newborns. This increase was not expected and forced us to reconsider when transient effects of the initial state would end. We hypothesize that it is due to effects of size-structured competition in this system. The results show that predictors of extinction probability can be shared between small and established populations. Transient dynamics of extinction risk can be long, with phases even mimicking a stationarity followed by the onset of an extinction vortex.

evolutionary biology↗

bioRxiv2024

Extinction probabilities of small structured populations: adequate short-term model predictions in Folsomia candida

Population management requires predictions of extinction risk based on a general understanding of these risks and on system-specific modelling. Life tables, available for numerous populations and species, permit calculating population growth and the construction of multi-type branching process models which predict population survivorship and ultimate extinction probabilities. We exemplify this approach and tailor it to an experimental model to predict extinction probabilities per unit of time. In age-structured populations, founders from different age classes lead to different predicted extinction probabilities. Age effects interact with environmental effects such as culling levels, which influence population growth rates. We assess the accuracy of predictions based on an age-structured matrix model, in an extinction experiment over an eight-week period on the springtail Folsomia candida, with crossed founder age and culling level treatments. Using parameter estimates from an accessory experiment, the fit of model predictions to observed extinction probabilities was generally good. A modified branching process model which allowed culling events between and at observations reduced prediction error. However, additionally maximizing the likelihood of observed extinction probabilities based on survival and fecundity parameters, or on a parameter which concentrated fecundity within a subinterval, did not significantly reduce prediction error according to the AICc. Our study shows that satisfactory predictions of establishment probabilities and of the initial persistence of small populations can be made using multi-type branching processes and available parameter estimates. Predictions can be improved by integrating knowledge of when events occur within intervals. This can be done without additional parameter estimation.

ecology↗

bioRxiv2021

CREB repressor in mushroom body enhances Drosophila LTM formation

Long-term memory (LTM) requires learning-induced synthesis of new proteins allocated to specific neurons and synapses in a neural circuit. Not all learned information, however, becomes permanent memory. How the brain gates relevant information into LTM remains unclear. In Drosophila adults, a single training session in an olfactory aversive task is not sufficient to induce protein synthesis-dependent LTM. Instead, multiple spaced training sessions are required. Here, we report that initial learning induces neural activity in the early /{beta} subset of Kenyon cells of the mushroom body (MB), and output from these neurons inhibits LTM formation. Specifically in response to spaced training, Schnurri activates CREBB expression which then appears to suppress the inhibitory output from MB. One training session can enhance LTM formation when this inhibitory effect is relieved. We propose that learning-induced protein synthesis and spaced training-induced CREBB act antagonistically to modulate output from early /{beta} MB neurons during LTM formation.

neuroscience↗

bioRxiv2019

From individuals to populations: How intraspecific competition shapes thermal reaction norms

O_LIMost ectotherms follow the temperature-size rule (TSR): in cold environments individuals grow slowly but reach a large asymptotic length. Intraspecific competition can induce plastic changes of growth rate and asymptotic length and competition may itself be modulated by temperature.\nC_LIO_LIOur aim is to disentangle the joint effects of temperature and intraspecific competition on growth rate and asymptotic length.\nC_LIO_LIWe used two distinct clonal lineages of the Collembola Folsomia candida, to describe thermal reaction norms of growth rate, asymptotic length and reproduction over 6 temperatures between 6{degrees}C and 29{degrees}C. In parallel, we measured the long-term size-structure and dynamics of populations reared under the same temperatures to measure growth rates and asymptotic lengths in populations and to quantify the joint effects of competition and temperature on these traits.\nC_LIO_LIWe show that intraspecific competition modulates the temperature-size rule. In dense populations there is a direct negative effect of temperature on asymptotic length, but there is no temperature dependence of the growth rate, the dominant factor regulating growth being competition. We fail to demonstrate that the strength of competition varies with temperature except at the lowest temperature where competition is minimal. The two lineages responded differently to the joint effects of temperature and competition and these genetic differences have marked effects on population dynamics along our temperature gradient.\nC_LIO_LIOur results reinforce the idea that the TSR response of ectotherms can be modulated by biotic and abiotic stressors when studied in non-optimal laboratory experiments. Untangling complex interactions between environment and demography will help understanding how size will respond to environmental change and how climate change may influence population dynamics.\nC_LI

ecology↗

bioRxiv2018

Robustness of bristle number to temperature and genetic background varies with bristle type and is regulated by miR-9a.

Robustness is the invariance of a given phenotype when faced with a given incoming genetic or environmental variation. Such essential property is being studied in a wide diversity of traits in many organisms but it is difficult to compare the results obtained on the robustness of different traits with each other given the differences that exist between traits in the way they are measured, in their genetic architecture and development. In this study, we assessed robustness of bristle number to incoming genetic and environmental variation for eight bristle types in the fruit fly Drosophila melanogaster, allowing for a straightforward comparison of the robustness observed between bristle types. We measured the response of bristle number mean and variance to changes in temperature and in the number of copies of two genes (scute and miR-9a) known to be involved in bristle development. Many combinations between the three factors were tested, thus allowing to test for the effect of each factor in different contexts for the two other factors - to which we refer herein as different backgrounds. We have found different responses between bristle types, suggesting that they present different levels of robustness to the factors tested. In addition, we have found that temperature and miR-9a affect more generally the variance of the traits rather than their means, thus fulfilling a criteria usually admitted to identify robustness factors.

genetics↗