Hypoglycemia risk with physical activity in type 1 diabetes: a data-driven approach.

Physical activity (PA) provides numerous health benefits for individuals with type 1 diabetes (T1D). However, the threat of exercise-induced hypoglycemia may impede the desire for regular PA. Therefore, we aimed to study the association between three common types of PA (walking, running, and cycling) and hypoglycemia risk in 50 individuals with T1D. Real-world data, including PA duration and intensity, continuous glucose monitor (CGM) values, and insulin doses, were available from the Tidepool Big Data Donation Project. Participants' mean (SD) age was 38.0 (13.1) years with a mean (SD) diabetes duration of 21.4 (12.9) years and an average of 26.2 weeks of CGM data available. We developed a linear regression model for each of the three PA types to predict the average glucose deviation from 70 mg/dl for the 2 h after the start of PA. This is essentially a measure of hypoglycemia risk, for which we used the following predictors: PA duration (mins) and intensity (calories burned), 2-hour pre-exercise area under the glucose curve (adjusted AUC), the glucose value at the beginning of PA, and total bolus insulin (units) within 2 h before PA. Our models indicated that glucose value at the start of exercise and pre-exercise glucose adjusted AUC (p < 0.001 for all three activities) were the most significant predictors of hypoglycemia. In addition, the duration and intensity of PA and 2-hour bolus insulin were weakly associated with hypoglycemia for walking, running, and cycling. These findings may provide individuals with T1D with a data-driven approach to preparing for PA that minimizes hypoglycemia risk.

Gill surface area allometry does not constrain the body mass scaling of maximum oxygen uptake rate in the tidepool sculpin, Oligocottus maculosus.

The gill oxygen limitation hypothesis (GOLH) suggests that hypometric scaling of metabolic rate in fishes is a consequence of oxygen supply constraints imposed by the mismatched growth rates of gill surface area (a two-dimensional surface) and body mass (a three-dimensional volume). GOLH may, therefore, explain the size-dependent spatial distribution of fish in temperature- and oxygen-variable environments through size-dependent respiratory capacity, but this question is unstudied. We tested GOLH in the tidepool sculpin, Oligocottus maculosus, a species in which body mass decreases with increasing temperature- and oxygen-variability in the intertidal, a pattern consistent with GOLH. We statistically evaluated support for GOLH versus distributed control of [Formula: see text] allometry by comparing scaling coefficients for gill surface area, standard and maximum [Formula: see text] ([Formula: see text],Standard and [Formula: see text],Max, respectively), ventricle mass, hematocrit, and metabolic enzyme activities in white muscle. To empirically evaluate whether there is a proximate constraint on oxygen supply capacity with increasing body mass, we measured [Formula: see text],Max across a range of Po2s from normoxia to Pcrit, calculated the regulation value (R), a measure of oxyregulatory capacity, and analyzed the R-body mass relationship. In contrast with GOLH, gill surface area scaling either matched or was more than sufficient to meet [Formula: see text] demands with increasing body mass and R did not change with body mass. Ventricle mass (b = 1.22) scaled similarly to [Formula: see text],Max (b = 1.18) suggesting a possible role for the heart in the scaling of [Formula: see text],Max. Together our results do not support GOLH as a mechanism structuring the distribution of O. maculosus and suggest distributed control of oxyregulatory capacity.

Low-pH seawater alters indirect interactions in rocky-shore tidepools.

Ocean acidification is expected to degrade marine ecosystems, yet most studies focus on organismal-level impacts rather than ecological perturbations. Field studies are especially sparse, particularly ones examining shifts in direct and indirect consumer interactions. Here we address such connections within tidepool communities of rocky shores, focusing on a three-level food web involving the keystone sea star predator, Pisaster ochraceus, a common herbivorous snail, Tegula funebralis, and a macroalgal basal resource, Macrocystis pyrifera. We demonstrate that during nighttime low tides, experimentally manipulated declines in seawater pH suppress the anti-predator behavior of snails, bolstering their grazing, and diminishing the top-down influence of predators on basal resources. This attenuation of top-down control is absent in pools maintained experimentally at higher pH. These findings suggest that as ocean acidification proceeds, shifts of behaviorally mediated links in food webs could change how cascading effects of predators manifest within marine communities.

Shifts in seawater chemistry disrupt trophic links within a simple shoreline food web.

Marine intertidal systems have long served as focal environments for ecological research, yet these environments are changing due to the entry of human-produced carbon dioxide into seawater, which causes 'ocean acidification' (OA). One component of OA is a decline in seawater pH, an alteration known to disrupt organism behaviors underlying predator-prey interactions. To date, however, studies examining OA's effects on feeding relationships consider predominantly simple direct interactions between consumers and their food sources. Here, we extended these established approaches to test how decreased seawater pH might alter cascading effects that span tiered linkages in trophic networks. We employed a model shoreline food web incorporating a sea star predator (Leptasterias hexactis), an herbivorous snail prey (Tegula funebralis), and a common macroalgal resource for the prey (Mazzaella flaccida). Results demonstrate direct negative effects of low pH on anti-predator behavior of snails, but also weakened indirect interactions, driven by increased snail consumption of macroalgae even as sea stars ate more snails. This latter outcome arose because low pH induced 'foolhardy' behaviors in snails, whereby their flight responses were supplanted by other activities that allowed for foraging. These findings highlight the potential for human-induced changes in seawater chemistry to perturb prey behaviors and trophic dynamics with accompanying community-level consequences.

Identification of the alternative oxidase gene and its expression in the copepod Tigriopus californicus.

In addition to the typical electron transport system (ETS) in animal mitochondria responsible for oxidative phosphorylation, in some species there exists an alternative oxidase (AOX) pathway capable of catalyzing the oxidation of ubiquinol and the reduction of oxygen to water. The discovery of AOX in animals is recent and further investigations into its expression, regulation, and physiological role have been hampered by the lack of a tractable experimental model organism. Our recent DNA database searches using bioinformatics revealed an AOX sequence in several marine copepods including Tigriopus californicus. This species lives in tidepools along the west coast of North America and is subject to a wide variety of daily environmental stresses. Here we verify the presence of the AOX gene in T. californicus and the expression of AOX mRNA and AOX protein in various life stages of the animal. We demonstrate that levels of the AOX protein increase in T. californicus in response to cold and heat stress compared to normal rearing temperature. We predict that a functional AOX pathway is present in T. californicus, propose that this species will be a useful model organism for the study of AOX in animals, and discuss future directions for animal AOX research.

Site fidelity and homing behaviour of intertidal sculpins revisited.

To assess the repeatability of an ecological study, this study both partially replicates and extends a previous study on the site fidelity and homing ability of two abundant and ecologically important species of rocky intertidal sculpin fishes, Oligocottus maculosus and Oligocottus snyderi. A traditional mark and recapture approach was utilized and found that both of these species display high site fidelity to a home range of tidepools and homing ability to these pools, confirming the findings of previous work. Unlike the previous study, however, there was no effect of body size on homing ability and a modelling approach that incorporates encounter probability provided evidence for a sex effect on homing ability. In addition, this study extends the maximum homing ability of O. snyderi to 179 m and O. maculosus to 218 m, which were the maximum displacement distances for each species in this study, suggesting they may be capable of even greater homing distances. This work, however, finds that homing success was negatively related to displacement distance. These findings suggest adult sculpin populations are likely to be highly sub-structured geographically, possibly contributing to the exceptionally high species richness of the group.

Shifts in intertidal zonation and refuge use by prey after mass mortalities of two predators.

Recent mass mortalities of two predatory sea star species provided an unprecedented opportunity to test the effect of predators on rocky intertidal prey. Mass mortalities provide insight that manipulative experiments cannot because they alter ecosystems on a larger scale, for longer time periods, and remove both organisms and their cues from the environment. We examined shifts in population size structure, vertical zonation, and use of emersed refuge habitats outside tidepools by the abundant herbivorous black turban snail Tegula funebralis, both before and after the successive mortalities of two predatory sea stars. The small cryptic predator Leptasterias spp. suffered a localized but extreme mortality event in November 2010, followed by two mass mortalities of the keystone predator Pisaster ochraceus in August 2011 and autumn 2013. After the local extinction of Leptasterias, the population size of Tegula more than doubled. Also, since Leptasterias primarily inhabited only mid to low intertidal tidepools at this site, small and medium sized snails (which are preferred by Leptasterias) shifted lower in the intertidal and into tidepools after the mortality of Leptasterias. After the mortality of Pisaster in August 2011, large snails did not shift lower in the intertidal zone despite being preferred by Pisaster. Small and medium sized snails became denser in the higher zone and outside tidepools, which was not likely due to Pisaster mortality. Previous studies concluded that Pisaster maintained vertical size gradients of snails, but our data implicate the overlooked predator Leptasterias as the primary cause. This natural experiment indicated that (1) predators exert top-down control over prey population sizes and lower limits, (2) vertical zonation of prey are dynamic and controlled in part by prey behavior, and (3) predators exert the strongest effects on more vulnerable individuals, which typically inhabit stressful habitats higher on the shore or outside tidepools to avoid predation. Because the mass mortalities of two predators drastically reduced both the predation pressure and the chemical cues of predators in the environment, we were able to investigate both the effects of predators on prey populations and the effects on mobile prey behavior.

Length-weight and length-length relationships for rockpool fishes on the Brazilian coast / Relações comprimento-peso e comprimento-comprimento para os peixes de poças de maré na costa brasileira

Abstract Fifty-nine length-weight (LWR) and length-length (LLR) relationships were estimated for 18 fish species, belonging to 10 families. The fish specimens were captured in rockpools of 21 sites along a stretch of 4,900 km of the Brazilian coast, between latitudes 00° and 22°S, in 2012. This study represents the first reference available for five fish species (Gobiesox barbatulus, Bathygobius geminatus, Labrisomus nuchipinnis, Malacoctenus delalandii, Lutjanus alexandrei) in LLR and six (Gobiesox barbatulus, Bathygobius geminatus, Hypleurochilus fissicornis, Omobranchus punctatus, Entomacrodus vomerinus, Diplodus argenteus) in LWR.

Resumo Cinquenta e nove relações peso-comprimento (RRC) e comprimento-comprimento (RCC) foram estimadas para 18 espécies de peixes, distribuídos em 10 famílias. Os espécimes de peixes foram capturados em poças de maré de 21 locais amostrados, ao longo de um trecho de 4.900 km da costa brasileira, entre as latitudes 00° e 22°S, durante o ano de 2012. Este estudo apresenta a primeira referência disponível para 5 espécies de peixes (Gobiesox barbatulus, Bathygobius geminatus, Labrisomus nuchipinnis, Malacoctenus delalandii, Lutjanus alexandrei) em RCC e 6 (Gobiesox barbatulus, Bathygobius geminatus, Hypleurochilus fissicornis, Omobranchus punctatus, Entomacrodus vomerinus, Diplodus argenteus) em RPC.

Ocean acidification alters the response of intertidal snails to a key sea star predator.

Organism-level effects of ocean acidification (OA) are well recognized. Less understood are OA's consequences for ecological species interactions. Here, we examine a behaviourally mediated predator-prey interaction within the rocky intertidal zone of the temperate eastern Pacific Ocean, using it as a model system to explore OA's capacity to impair invertebrate anti-predator behaviours more broadly. Our system involves the iconic sea star predator, Pisaster ochraceus, that elicits flee responses in numerous gastropod prey. We examine, in particular, the capacity for OA-associated reductions in pH to alter flight behaviours of the black turban snail, Tegula funebralis, an often-abundant and well-studied grazer in the system. We assess interactions between these species at 16 discrete levels of pH, quantifying the full functional response of Tegula under present and near-future OA conditions. Results demonstrate the disruption of snail anti-predator behaviours at low pH, with decreases in the time individuals spend in refuge locations. We also show that fluctuations in pH, including those typical of rock pools inhabited by snails, do not materially change outcomes, implying little capacity for episodically benign pH conditions to aid behavioural recovery. Together, these findings suggest a strong potential for OA to induce cascading community-level shifts within this long-studied ecosystem.

The role of macrobiota in structuring microbial communities along rocky shores.

Rocky shore microbial diversity presents an excellent system to test for microbial habitat specificity or generality, enabling us to decipher how common macrobiota shape microbial community structure. At two coastal locations in the northeast Pacific Ocean, we show that microbial composition was significantly different between inert surfaces, the biogenic surfaces that included rocky shore animals and an alga, and the water column plankton. While all sampled entities had a core of common OTUs, rare OTUs drove differences among biotic and abiotic substrates. For the mussel Mytilus californianus, the shell surface harbored greater alpha diversity compared to internal tissues of the gill and siphon. Strikingly, a 7-year experimental removal of this mussel from tidepools did not significantly alter the microbial community structure of microbes associated with inert surfaces when compared with unmanipulated tidepools. However, bacterial taxa associated with nitrate reduction had greater relative abundance with mussels present, suggesting an impact of increased animal-derived nitrogen on a subset of microbial metabolism. Because the presence of mussels did not affect the structure and diversity of the microbial community on adjacent inert substrates, microbes in this rocky shore environment may be predominantly affected through direct physical association with macrobiota.

Tidepool fish assemblages of Gorgona Island, Colombian Pacific coast: a local and regional comparison / Ensambles de peces de poza de isla Gorgona, costa pacífica colombiana: una comparación local y regional

The ecology of tidepool fishes has been extensively investigated worldwide over the past 40 years. As in many other ecological fields, studies in temperate zones outnumber studies carried out in tropical areas. Here, we document the short-term spatio-temporal variation of a tidepool fish assemblage from the Tropical Eastern Pacific (Gorgona Island, Colombia), compare our data with previous surveys made in 1993 and provide the first latitudinal comparison of tidepool fish assemblages in the Eastern Pacific coast (43°N to 36°S). During April-July 2006, monthly samplings were carried in 18 tidepools located at three sites this Island. A relatively species-rich tidepool fish assemblage (53 species) was found at Gorgona Island. Labrisomidae, Gobiidae and Gobiesocidae were the dominant resident components of this assemblage, whereas Pomacentridae, Muraenidae and Labridae constituted the transient component. Although the same dominant species were observed in surveys from 1993 and 2006, suggesting a high persistence of this assemblage over time, clear differences in the relative abundance of some species were also detected. These differences were partly the result of using different sampling methodologies (rotenone vs clove oil). Comparisons with other studies performed in tropical and temperate areas of the Eastern Pacific coast indicate a clear latitudinal pattern in the composition of these assemblages that correspond to well-documented biogeographic subdivisions of the marine fauna in this region. Further investigation of the ecological role that tidepool fishes play in rocky intertidal and subtidal areas of Gorgona Island and the whole Tropical Eastern Pacific region will benefit our understanding of the functioning of these important coastal ecosystems. Rev. Biol. Trop. 62 (Suppl. 1): 373-390. Epub 2014 February 01.

A nivel mundial, la ecología de peces de charcos intermareales ha sido ampliamente investigada durante los últimos 40 años, especialmente en zonas templadas. En este trabajo, se documenta la variación espacio-temporal en corta escala de un ensamblaje de peces de charcos intermareales en el Pacífico Oriental Tropical (Isla Gorgona, Colombia), y se comparan nuestros resultados, con los resultados obtenidos durante muestreos realizados en la misma localidad en 1993. Además se realiza la primera comparación latitudinal de estos ensamblajes para la costa oriental del Océano Pacífico (43°N a 36°S). Durante abril a junio de 2006, se realizaron muestreos mensuales en 18 charcos intermareales distribuidos en tres localidades de Isla Gorgona, estableciendo un ensamblaje de peces de charcos intermareales con una alta riqueza de especies (53 especies). Labrisomidae, Gobiidae and Gobiesocidae fueron los componentes residentes dominantes en el ensamblaje, mientras que Pomacentridae, Muraenidae and Labridae fueron los componentes transitorios. Aunque el registro de las mismas especies dominantes en 1993 y 2006 sustenta la idea de una alta persistencia temporal de este ensamblaje, se detectaron diferencias significativas en la abundancia relativa de las especies. Estas diferencias podrían ser el resultado de las diferentes técnicas de captura utilizadas durante 1993 y 2006 (rotenona vs aceite de clavo). Al comparar los estudios sobre peces intermareales realizados en la zona tropical y zona templada de la costa oriental del Océano Pacífico, se identificó un claro patrón latitudinal en la composición de los ensamblajes, que es consecuente con la ampliamente documentada subdivisión biogeográfica de la fauna marina de esta región. Para comprender el funcionamiento de los ecosistemas costeros del Pacífico Oriental tropical, es necesario que futuros esfuerzos de investigación se encaminen a conocer el papel ecológico de los peces intermareales en esta región.

Physiological performance of intertidal coralline algae during a simulated tidal cycle.

Intertidal macroalgae endure light, desiccation, and temperature variation associated with sub-merged and emerged conditions on a daily basis. Physiological stresses exist over the course of the entire tidal cycle, and physiological differences in response to these stresses likely contribute to spatial separation of species along the shore. For example, marine species that have a high stress tolerance can live higher on the shore and are able to recover when the tide returns, whereas species with a lower stress tolerance may be relegated to living lower on the shore or in tidepools, where low tide stresses are buffered. In this study, we monitored the physiological responses of the tidepool coralline Calliarthron tuberculosum (Postels and Ruprecht) E.Y. Dawson and the nontidepool coralline Corallina vancouveriensis Yendo during simulated tidal conditions to identify differences in physiology that might underlie differences in habitat. During high tide, Corallina was more photosynthetically active than Calliarthron as light levels increased. During low tide, Corallina continued to out-perform Calliarthron when submerged in warming tidepools, but photosynthesis abruptly halted for both species when emerged in air. Surprisingly, pigment composition did not differ, suggesting that light harvesting does not account for this difference. Additionally, Corallina was more effective at resisting desiccation by retaining water in its branches. When the tide returned, only Corallina recovered from combined temperature and desiccation stresses associated with emergence. This study broadens our understanding of intertidal algal physiology and provides a new perspective on the physiological and morphological underpinnings of habitat partitioning.

Temporal and spatial variations in tidepool fish assemblages of the northeast coast of Brazil / Variação espacial e temporal na fauna de peixes em poças de maré do nordeste do Brasil

Temporal and spatial variations and environmental factors influencing the structure of tidepool fish assemblages were quantitatively investigated at Iparana beach, northeast Brazilian coast. The majority of the tidepool fishes sampled were suprabenthic juvenile individuals of great mobility. We recorded during monthly diurnal underwater visual censuses a total of 4,750 fish from 26 species, represented mainly by partial residents from the families Scaridae, Haemulidae, Gerreidae and Pomacentridae. The number of species and individuals showed significant variability among tidepools as a response to variations in their volume and type of substrate cover. The greatest species abundance and richness associated with rocks covered with algae suggested that substrate complexity is one of the main factors defining the spatial structure of the tidepool ichthyofauna. Temporal variability in species abundance and richness was associated with changes in salinity levels due to seasonal rainfalls. A higher number of juvenile fishes from December to May in our samples corroborate the hypothesis that the tidepools act as nursery sites. Therefore, the species associations found in this study and their relation to seasonal and spatial discontinuities may be partly explained according to their habitat requirements and reproductive cycles.

Investigamos quantitativamente variações espaciais e temporais, assim como os fatores ambientais que podem influenciar a estrutura da fauna de peixes em poças de maré da praia de Iparana, nordeste do Brasil. A maioria dos peixes registrados eram indivíduos suprabênticos jovens de grande mobilidade. Registramos, através de censos visuais subaquáticos diurnos mensais, um total de 4.750 peixes pertencentes a 26 espécies, representados principalmente por residentes parciais das famílias Scaridae, Haemulidae, Gerreidae e Pomacentridae. Os números de espécies e indivíduos mostraram variação significativa entre as poças amostradas com relação ao seu volume e tipo de cobertura do substrato. As maiores abundância e riqueza de espécies foram associadas à presença de rochas cobertas com algas, sugerindo que a complexidade estrutural do substrato é um dos principais fatores que define a estrutura espacial da ictiofauna em poças de marés. A variabilidade temporal em abundância e riqueza de espécies foi associada com variações de salinidade devido à sazonalidade das chuvas. Um maior número de peixes jovens registrados entre dezembro e maio corrobora a hipótese de que as poças de maré funcionam como berçários. Portanto, as associações de espécies encontradas neste estudo, assim como suas relações de descontinuidades sazonais e espaciais podem ser explicadas parcialmente de acordo com as exigências de hábitat e ciclos reprodutivos.