Biology subjects

Purchase, C.

Publications and source records attributed to Purchase, C..

4 recordsLinked to original sources

bioRxiv2026

Investigating biotic, chemical, and physical drivers of periphyton and invertebrate biomass in boreal streams supporting juvenile Atlantic salmon

1. Atlantic salmon (Salmo salar) are an anadromous fish with a broad distribution from eastern North America to western Europe, with ecological, economic, and cultural significance. Despite their expansive range, wild populations across the North Atlantic have experienced decline. Survival to reproductive age is a management concern, with a focus on identifying factors affecting the juvenile freshwater life stage. Specifically, research is needed to identify potential bottlenecks limiting freshwater productivity. 2. We addressed this research gap with a case study on the Exploits River, Newfoundland - a watershed that receives one of the largest anadromous Atlantic salmon returns in North America. We aimed to identify biotic, chemical, and physical predictors of food resources for juvenile salmon (i.e., invertebrates) and food resources for invertebrates (i.e., periphyton). To test our hypotheses, we collected data on a suite of biotic (e.g., invertebrates and periphyton), chemical (e.g., total dissolved N), and physical (e.g., wetted width) variables at 42 sites within and around this watershed. 3. We observed evidence for relationships between invertebrate biomass and biotic and temporal variables. Specifically, invertebrate biomass was higher at sites with high periphyton biomass that were sampled later in the season. In addition, we observed that periphyton biomass was related to biotic, chemical, and physical variables. Here, we present evidence for bottom-up control, with increased periphyton biomass supporting increased invertebrate biomass. 4. We expect knock-on effects where increased invertebrate biomass results in increased juvenile Atlantic salmon biomass. Our large sample size revealed some predictors of invertebrate biomass and periphyton biomass. However, we found no evidence of correlation between invertebrate biomass and chemical or physical variables. The low productivity of our maritime boreal forest system could be an outlier in expected biotic, chemical, and physical relationships in streams. 5. Our findings provide an important step forward in furthering boreal stream ecology, producing novel invertebrate and periphyton knowledge for watershed managers.

ecology↗

bioRxiv2025

How monitoring behavior can inform conservation? The case of Spix's macaws under human care

The Spixs macaw (Cyanopsitta spixii), extinct in the wild since 2019, is currently maintained in exsitu breeding facilities. Captive breeding expanded the global population from 53 individuals in 2000 to ca. 400 by December 2025, enabling two soft releases. To support reintroduction, we introduce an ethogram of 85 behaviours and 1357 quantitative records based on observations of 123 birds at the ACTP Germany facility. Based on the analysis of the time-activity patterns of 10 pairs for 17 hours each, we also explore whether behavioural compatibility during the non-breeding season--measured here as time-activity similarity--relates to the breeding output of these pairs. Individual activity patterns were consistent, but females were markedly more synchronised with their mates than with other males. However, only pairs showing a high time-activity similarity bred successfully. Adjusting pair matching based on such similarity and improving general husbandry conditions (diet & enrichment) led to higher breeding output: pairs raising chicks increased from 0 in 2019 to 16 in 2024, fertility rates increased from 27% in 2019 to 64% in 2024, and annual chick output increased from 11 to 44 between 2019 and 2024. These results, based on 86 forced-mating attempts, support the idea that systematic behavioural monitoring can substantially contribute to enhancing conservation breeding in monogamous parrot species.

animal behavior and cognition↗

bioRxiv2022

Frequency-dependent viscosity of salmon ovarian fluid has biophysical implications for sperm-egg interactions

Gamete-level sexual selection of externally fertilising species is usually achieved by modifying sperm behaviour with mechanisms thought to alter the chemical environment in which gametes perform. In fish this can be accomplished through the ovarian fluid, a substance released with the eggs at spawning. While its biochemical effects in relation to sperm energetics have been investigated, the influence of the physical environment in which sperm compete remains poorly explored. Our objective was therefore to gain insights on the physical structure of this fluid and potential impacts on reproduction. Using soft-matter physics approaches of steady-state and oscillatory viscosity measurements, we subjected salmon ovarian fluids to variable shear stresses and frequencies resembling those exerted by sperm swimming through the fluid near eggs. We show that this fluid, which in its relaxed state is a gel-like substance, displays a non-Newtonian viscoelastic and shear-thinning profile, where the viscosity decreases with increasing shear rates. We concurrently find that this fluid obeys the Cox-Merz rule below 7.6 Hz and infringes it above, thus indicating a shear-thickening phase where viscosity increases provided it is probed gently enough. This suggests the presence of a unique frequency-dependant structural network with relevant implications on sperm energetics and fertilisation dynamics.

evolutionary biology↗

bioRxiv2022

Evidence of hatch-time based growth compensation in the early life history of two salmonid fishes

Initial body size can indicate quality within-species, with large size increasing the likelihood of survival. However, some populations or individuals may have body size disadvantages due to spatial/temporal differences in temperature, photoperiod, or food availability. Across-populations animals often have locally adapted physiology to compensate for poor environmental influences on development and growth, while within-populations behavioural adjustments that increase food intake after periods of deprivation provide opportunities to catch up (growth compensation). We posit a theoretical extension of growth compensation to include within-population differences related to short growing seasons due to delayed hatch time. We tested the hypothesis that individual fish that hatch later grow faster than those that hatch earlier. The relative magnitude of such a response was compared to growth variation among populations and between related species. We sampled young of the year Arctic charr and brook trout from five rivers in northern Labrador. Daily increments from otoliths were used to back-calculate size to a common age and calculate growth rates. Supporting the hypothesis, older fish were not larger at capture than younger fish, because animals that hatched later grew faster which may indicate age-based growth compensation.

ecology↗