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Many traits important for reproductive isolation are environmentally responsive. However, most studies examining reproductive isolation do not explicitly take into consideration environmental variation. Temperature can have a particularly large effect on reproductive behaviours, especially in ectotherms. Here, we tested whether temperature affects the degree of reproductive isolation between the upland chorus frog, Pseudacris feriarum, and its congener Pseudacris nigrita. These two species engage in costly hybridization in nature, leading to reinforcement of male signals and female preferences in sympatry. However, male advertisement calls vary with temperature such that the difference between the advertisement calls of the two species is narrower at cold temperatures than at warm temperatures. To examine the effect of temperature on reproductive isolation in this system, we performed six binary choice preference trials using sympatric female P. feriarum. In these experiments, we acclimated females to either warm (20 °C) or cool (10 °C) temperatures and gave them a choice between heterospecific and conspecific advertisement calls appropriate for the temperature. We also conducted experiments where we gave females a choice between more similar stimuli at warm temperatures to test whether females have narrower preferences at cold temperatures. We found that females always had a significant preference for the conspecific advertisement call, regardless of temperature or signal similarity. However, females took twice as long to make a choice in suboptimal conditions. This time delay may lead to increased risk of hybridization, despite females’ ability to discriminate between calls. Our results highlight the importance of considering environmental context when examining traits involved in reproductive isolation.
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Heat tolerance and thermal preference of the copepod Tigriopus californicus are insensitive to ecologically relevant dissolved oxygen levels
Abstract Shifting climate patterns may impose novel combinations of abiotic conditions on animals, yet understanding of the present-day interactive effects of multiple stressors remains under-developed. We tested the oxygen and capacity limited thermal tolerance (OCLTT) hypothesis and quantified environmental preference of the copepod Tigriopus californicus , which inhabits rocky-shore splashpools where diel fluctuations of temperature and dissolved oxygen (DO) are substantial. Egg-mass bearing females were exposed to a 5 h heat ramp to peak temperatures of 34.1–38.0 °C crossed with each of four oxygen levels: 22, 30, 100 and 250% saturation (4.7–5.3, 5.3–6.4, 21.2–21.3, and 50.7–53.3 kPa). Survival decreased at higher temperatures but was independent of DO. The behavioral preference of females was quantified in seven combinations of gradients of both temperature (11–37 °C) and oxygen saturation (17–206% or 3.6–43.6 kPa). Females avoided high temperatures regardless of DO levels. This pattern was more pronounced when low DO coincided with high temperature. In uniform temperature treatments, the distribution shifted toward high DO levels, especially in uniform high temperature, confirming that Tigriopus can sense environmental p O 2 . These results question the ecological relevance of OCLTT for Tigriopus and raise the possibility of microhabitat selection being used within splashpool environments to avoid physiologically stressful combinations of conditions.
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- Award ID(s):
- 1655822
- PAR ID:
- 10215426
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Environments with fluctuating oxygen are intense challenges for organisms both on land and in the water. Aquatic organisms can be exposed to especially stressful bouts of hypoxia that come on rapidly and to extreme levels. The copepodTigriopus californicusinhabits supralittoral rocky pools and appears tolerant of hypoxia levels considered lethal for other aquatic organisms despite lacking molecular components typically used by animals to detect and respond to low environmental oxygen. Here, we quantified the natural regime of dissolved oxygen (DO) pools inhabited byT. californicusvia deployment of continuous oxygen sensors in copepod pools in Oregon, USA. Using wild-derived cultures from northern (Oregon) and southern (Californian) populations, we exposed copepods to hypoxia and anoxia and assayed loss of equilibrium (LOE) and survival. We also quantified respiratory regulation via critical oxygen tension, oxygen supply capacity, and regulation index. The pools underwent extreme daily cycles of DO, and near anoxia often persisted for up to 6 h. Respiratory statistics indicated individuals could regulate oxygen consumption even near anoxia, predicting a species with hypoxia tolerance ranking high among aquatic taxa. Copepods survived hypoxia below 0.3 mg O2l-1for up to 72 h with some individuals not showing any LOE. Survival was high following even 6 and 15 h exposure to anoxia. We observed sex and population differences in lethality and LOE, with southern populations exhibiting higher resilience. Intraspecific variation in tolerance makes this system a candidate for future studies to investigate alternative molecular and physiological pathways of hypoxia response.more » « less
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Abstract The mysid Neomysis americana (Smith, 1873) is native to shallow shelf waters and estuaries of the western Atlantic coast of North America. Despite the important role mysids such as N. americana play in estuarine ecosystems as both consumers and as prey for higher trophic levels, there is limited information on how metabolism influences their spatial ecology and habitat requirements. In tributaries of Chesapeake Bay, MD, USA, previous research has shown that summer water temperatures can approach the lethal upper tolerance limit for N. americana. We measured the per capita metabolic rate (µgO2 min–1) of N. americana from the upper Patuxent River near Benedict, MD, a tributary of Chesapeake Bay in the laboratory to evaluate the metabolic response to salinity and temperature conditions that mysids experience in natural habitats. Sex-specific and diel patterns in metabolic rate were quantified. Metabolic rates did not differ between night and day and there was no significant difference in metabolic rate between males and females, exclusive of gravid females. Metabolic rates were lowest in salinity treatments of 2 and 8 at 29 °C, and highest in the salinity 2 treatment at 22 °C. Only temperature had a statistically significant, albeit unexpected, effect. This study shows that the metabolic response of N. americana to temperature and salinity conditions is complex and plastic, and that metabolic rates can vary 3–4 fold within realistic summer temperature and salinity conditions. As environmental conditions continue to change, understanding metabolic response of mysids to realistic salinity and temperature conditions is necessary for understanding their distributions in temperate estuaries.more » « less
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Abstract Variation in temperature can affect the expression of a variety of important fitness‐related behaviours, including those involved with mate attraction and selection, with consequences for the coordination of mating across variable environments. We examined how temperature influences the expression of male mating signals and female mate preferences—as well as the relationship between how male signals and female mate preferences change across temperatures (signal–preference temperature coupling)—inEnchenopa binotatatreehoppers. These small plant‐feeding insects communicate using plantborne vibrations, and our field surveys indicate they experience significant natural variation in temperature during the mating season. We tested for signal–preference temperature coupling in four populations ofE. binotataby manipulating temperature in a controlled laboratory environment. We measured the frequency of male signals—the trait for which females show strongest preference—and female peak preference—the signal frequency most preferred by females—across a range of biologically relevant temperatures (18°C–36°C). We found a strong effect of temperature on both male signals and female preferences, which generated signal–preference temperature coupling within each population. Even in a population in which male signals mismatched female preferences, the temperature coupling reinforces predicted directional selection across all temperatures. Additionally, we found similar thermal sensitivity in signals and preferences across populations even though populations varied in the mean frequency of male signals and female peak preference. Together, these results suggest that temperature variation should not affect the action of sexual selection via female choice, but rather should reinforce stabilizing selection in populations with signal–preference matches, and directional selection in those with signal–preference mismatches. Finally, we do not predict that thermal variation will disrupt the coordination of mating in this species by generating signal–preference mismatches at thermal extremes.more » « less
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Abstract Predicting dissolved oxygen (DO) in lakes is important for assessing environmental conditions as well as reducing water treatment costs. High levels of DO often precede toxic algal blooms, and low DO causes carcinogenic metals to precipitate during water treatment. Typically, DO is predicted from limited data sets using hydrodynamic modeling or data‐driven approaches like neural networks. However, functional data analysis (FDA) is also an appropriate modeling paradigm for measurements of DO taken vertically through the water column. In this analysis, we build FDA models for a set of profiles measured every 2 hours and forecast the entire DO percent saturation profile from 2 to 24 hours ahead. Functional smoothing and functional principal component analysis are applied first, followed by a vector autoregressive model to forecast the empirical functional principal component (FPC) scores. Rolling training windows adapt to seasonality, and multiple combinations of window sizes, model variables, and parameter specifications are compared using both functional and direct root mean squared error metrics. The FPC method outperforms a suite of comparison models, and including functional pH, temperature, and conductivity variables improves the longer forecasts. Finally, the FDA approach is useful for identifying unusual observations.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41598-020-75635-z
