Land management explains major trends in forest structure and composition over the last millennium in California's Klamath Mountains.

SignificanceWe provide the first assessment of aboveground live tree biomass in a mixed conifer forest over the late Holocene. The biomass record, coupled with local Native oral history and fire scar records, shows that Native burning practices, along with a natural lightning-based fire regime, promoted long-term stability of the forest structure and composition for at least 1 millennium in a California forest. This record demonstrates that climate alone cannot account for observed forest conditions. Instead, forests were also shaped by a regime of frequent fire, including intentional ignitions by Native people. This work suggests a large-scale intervention could be required to achieve the historical conditions that supported forest resiliency and reflected Indigenous influence.

Growth and physiological responses in largemouth bass populations to environmental warming: Effects of inhabiting chronically heated environments.

Ectotherms are susceptible to increasing environmental temperatures associated with anthropogenic warming. Supra-optimum temperatures lead to declining aerobic capacity and can increase exposure to lethal temperatures, resulting in reduced performance. Although the capacity of phenotypic plasticity to minimize the effects of temperature on physiological processes is well studied, evidence of generational changes (e.g. transgenerational plasticity and rapid adaptation) in response to environmental warming is limited in natural populations. We investigated metabolism, growth, and thermal tolerance of largemouth bass (Micropterus salmoides) populations inhabiting thermally altered lakes (i.e. power plant cooling lakes) which have year-round elevated temperature regimes and exhibit supra-optimum temperatures on a yearly basis, and compared these traits with those in largemouth bass populations from ambient lakes. Largemouth bass from ambient and heated groups (n = 3 populations per group) were spawned in an ambient, common garden pond environment, then acclimated to either a normal summertime temperature (24 °C) or a supra-optimum temperature (30 °C). Fish from heated populations had significant reductions in the resting metabolic rate at both temperatures and markedly increased growth rates at 30 °C. By comparing pond-raised fish to fish removed directly from heated lakes, we showed that developmental plasticity played little role in establishing the metabolic rate. A lower resting metabolic rate contributed to an increase in the conversion efficiency of food to biomass of largemouth bass from heated lakes, regardless of temperature. Despite inhabiting heated lakes for many decades, neither critical thermal maximum nor minimum were altered in heated populations when raised in a common garden environment. These results suggest that largemouth bass can lessen sub-lethal effects of warming by altering physiological processes to reduce the impact of warming on aerobic scope and that these changes are generationally transient, but changes in maximum thermal tolerance in response to warming is limited to phenotypic plasticity.

Examining the effects of chronic, lake-wide elevated temperatures on behavioural expression in largemouth bass, Micropterus salmoides.

Many behaviours have differential fitness consequences across thermal and ecological contexts, indicating that both ecological shifts and warming temperatures induced by climatic change may alter how organisms behave. However, empirical evidence of temperature-driven behavioural selection in natural systems is lacking. We compared behaviours and behavioural syndromes related to activity, exploration, boldness and aggression in populations of largemouth bass (Micropterus salmoides) from ambient lakes to the those from artificially warmed, power plant cooling lakes to investigate changes in behaviours associated with warmer environments. Activity, exploration, boldness and aggression of juvenile largemouth bass were assessed in laboratory conditions using a novel environment assay and a risky situation assay. We found that activity and exploratory behaviours were higher and decreased through first year ontogeny in populations from heated lakes, whereas these behaviours were lower and showed no relationship through ontogeny in populations from ambient lakes. We attribute these differences to the changes in food source availability in heated lakes associated with temperature-driven ecological effects. Bold and aggressive behaviours tended to differ between populations, as did correlations between behaviours, but did not differ between ambient and heated lakes. The findings of this work identify that large ecological changes associated with warming environments, such as food availability, may drive changes in some aspects of behavioural expression in largemouth bass but that other aspects of behavioural expression may be driven by lake-specific factors not related to warming.

Invasive planktivores as mediators of organic matter exchanges within and across ecosystems.

Bighead carp (Hypophthalmichthys nobilis) are an invasive planktivore that can greatly deplete planktonic resources. Due to the inefficient conversion of food into fish tissue, large portions of consumed materials are egested and shunted to benthic habitats. We explored how bighead carp alter pools of organic matter between planktonic and benthic habitats, and across ecosystem boundaries. Here, we report evidence from a manipulative experiment demonstrating that bighead carp greatly reapportion pools of organic matter from planktonic to benthic habitats to such a degree that additional effects propagated across ecological boundaries into terrestrial ecosystems. Strong direct consumption by bighead carp reduced filamentous algae, biomass and production of zooplankton, and production of a native planktivorous fish within planktonic habitats. Reduced herbivory indirectly increased phytoplankton (chlorophyll a). Direct consumption of organic matter by bighead carp supported high carp production and concomitant losses of materials due to egestion. Perhaps in response to organic matter subsidies provided by fish egestion, ponds having bighead carp had higher standing crop biomass of Chironomidae larvae, as well as cross-boundary fluxes of their adult life stage. In contrast, we detected reduced cross-boundary fluxes of adult Chaoboridae midges in ponds having bighead carp. Consideration of bighead carp as mediators of organic matter exchanges provides a clearer framework for predicting the direct and extended impacts of these invasive planktivores in freshwater ecosystems. The perception of bighead carp must evolve beyond competitors for planktonic resources, to mediators and processors of nutrients and energy within and across ecosystems.

Does prey community composition affect the way different behavioral types interact with their environment?

We examined how different exploratory behavioral types of largemouth bass responded to differing prey communities by determining effects on growth, survival and diet in experimental ponds. We found evidence that non-explorer largemouth bass target young-of-year bluegill early on in life, but bluegill were not an important diet item by late summer. The presence of young-of-year bluegill as prey does appear to affect the foraging strategy of the two exploring types differently. In the absence of small bluegill, both behavioral types feed primarily on benthic invertebrates and zooplankton. When small bluegill were present, we saw a shift away from zooplankton as prey for largemouth bass. However, that shift was toward more benthic invertebrates for non-exploring behavioral types and toward terrestrial insects for exploring behavioral types. Thus, it appears that prey community composition can have important effects on the way in which different behavioral types interact with their environment.

Recreational fishing selectively captures individuals with the highest fitness potential.

Fisheries-induced evolution and its impact on the productivity of exploited fish stocks remains a highly contested research topic in applied fish evolution and fisheries science. Although many quantitative models assume that larger, more fecund fish are preferentially removed by fishing, there is no empirical evidence describing the relationship between vulnerability to capture and individual reproductive fitness in the wild. Using males from two lines of largemouth bass (Micropterus salmoides) selectively bred over three generations for either high (HV) or low (LV) vulnerability to angling as a model system, we show that the trait "vulnerability to angling" positively correlates with aggression, intensity of parental care, and reproductive fitness. The difference in reproductive fitness between HV and LV fish was particularly evident among larger males, which are also the preferred mating partners of females. Our study constitutes experimental evidence that recreational angling selectively captures individuals with the highest potential for reproductive fitness. Our study further suggests that selective removal of the fittest individuals likely occurs in many fisheries that target species engaged in parental care. As a result, depending on the ecological context, angling-induced selection may have negative consequences for recruitment within wild populations of largemouth bass and possibly other exploited species in which behavioral patterns that determine fitness, such as aggression or parental care, also affect their vulnerability to fishing gear.

Is winter worse for stressed fish? The consequences of exogenous cortisol manipulation on over-winter survival and condition of juvenile largemouth bass.

Over-winter mortality is an important selective force for warm-water fish (e.g., centrarchids) that live in temperate habitats. Inherent challenges faced by fish during winter may be compounded by additional stressors that activate the hypothalamic-pituitary-interrenal axis, either before or during winter, leading to negative sub-lethal impacts on fish health and condition, and possibly reducing chance of survival. We used experimental cortisol manipulation to test the hypothesis that juvenile largemouth bass (Micropterus salmoides) exposed to semi-chronic elevation in cortisol prior to winter would experience higher levels of over-winter mortality, physiological alterations and impaired immune status relative to control and sham-treated bass. Over-winter survival in experimental ponds was high, averaging 83%, and did not differ among treatment groups. Over the study period, bass exhibited an average increase in mass of 19.4%, as well as a slight increase in Fulton's condition factor, but neither measure differed among groups. Hepatosomatic index in cortisol-treated bass was 23% lower than in control fish, suggesting lower energy status, but white muscle lipid content was similar across all groups. Lastly, there was no difference in spleen somatic index or parasite load among treatment groups, indicating no long-term immune impairment related to our cortisol manipulation. The current study adds to a growing body of literature on glucocorticoid manipulations where field-based findings are not consistent with laboratory-based conceptual understanding of multiple stressors. This suggests that field conditions may provide fish with opportunities to mitigate negative effects of some stressors.

Response of largemouth bass (Micropterus salmoides) from different thermal environments to increased water temperature.

Due to concerns of global climate change, additional research is needed to quantify the thermal tolerance of species, and how organisms are able to adapt to changes in thermal regime. We quantified the thermal tolerance and thermal stress response of a temperate sportfish from two different thermal environments. One group of largemouth bass (Micropterus salmoides) inhabited thermally enhanced reservoirs (used for power plant cooling), with water temperatures typically 2-5°C warmer than nearby reservoirs. We tested fish for chronic thermal maxima and reaction to an 8°C heat shock using three common physiological indices of stress. We observed no evidence of differences between groups in thermal maxima. We observed no differences in thermal maxima between fish from artificially warmed and natural systems. Our results disagree with research, suggesting differences due to adaptation to different thermal environments. We speculate that behavioral modifications, lack of adequate time for genetic divergence, or the robust genetic plasticity of largemouth bass explain the lack of difference between treatment groups.

Acclimation to a low oxygen environment alters the hematology of largemouth bass (Micropterus salmoides).

One of the most severe impacts of urbanization on aquatic systems is the increasing presence of low oxygen environments caused by anthropogenic sources of pollution. As urbanization increases nationally and globally, it is becoming exceedingly important to understand how hypoxia affects aquatic fauna, especially fish species. In an effort to better understand the impacts of prolonged hypoxia on fishes, largemouth bass were held at 3.0 and 9.0 mg L⁻¹ for 50 days, which has previously shown to be temporally sufficient to impart plastic phenotypic changes. Following the holding period, fish from each group were subjected to a low dissolved oxygen (DO) challenge of 2.0 mg L⁻¹ for 6 h, and their physiological and hematological parameters were compared with control fish held for 6 h with no change in DO. There were no differences in the physiological stress responses between the two holding groups; however, the low oxygen holding group had increased hemoglobin and hematocrit levels following the 6-h low oxygen challenge compared with the high oxygen group. These results suggest largemouth bass exposed to chronic low oxygen conditions, either naturally or anthropogenically, may possess a beneficial advantage of increased oxygen uptake capacity during periods of low oxygen.

Independent age estimates resolve the controversy of ancient human footprints at White Sands.

Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected from the same stratigraphic horizons as those of the Ruppia seeds, along with optically stimulated luminescence ages of sediments from within the human footprint-bearing sequence, to evaluate the veracity of the seed ages. The results show that the chronologic framework originally established for the White Sands footprints is robust and reaffirm that humans were present in North America during the Last Glacial Maximum.

Influence of behavior and mating success on brood-specific contribution to fish recruitment in ponds.

One source of uncertainty in predicting the response of populations to exploitation is individual differences within a population in both vulnerability to capture and contribution to population renewal. For species with parental care, individuals engaged in nesting behavior are often targeted for exploitation, but predicting outcomes of this nonrandom vulnerability will depend in part on an understanding of how parental traits are related to potential for brood contribution to the population. Variation in brood-specific contribution to recruitment of largemouth bass (Micropterus salmoides), a fish species with extended parental care, was quantified to determine if differences in mating success, parental care behaviors, and timing of reproduction influenced offspring recruitment. Dependence of these relationships on brood predation was tested in communities that differed in the presence of bluegill, Lepomis macrochirus, an important nest predator. Daily snorkel surveys were conducted in experimental ponds during spring to monitor male spawning and parental care behaviors in populations of largemouth bass. Tissue samples collected from larvae in nests were used to develop brood-specific DNA fingerprints for determining nest origins of fall recruits. Largemouth bass spawning period in bluegill ponds was longer and more variable in duration, with lower, more variable mating success, than in ponds without bluegill. In all populations, only one or two broods provided the majority of recruits, and these were broods produced during the earliest days of spawning by the oldest, largest males. In bluegill ponds, brood contribution from earliest nests also increased with brood size. Earliest nesters were the oldest males, and recruits from these nests were often above average in body size. Offspring needed to be guarded to at least swim-up larval stage to contribute any recruits. Termination of parental protection before offspring were free swimming mainly occurred with broods guarded by smaller males in ponds with brood predators. These age- and size-specific differences in timing of spawning and duration of parental care are consistent with influences of residual reproductive value and energetic constraints on reproductive behavior. Furthermore, these patterns of individual contribution to recruitment imply that fisheries that selectively target either nesting individuals or larger, older males could potentially decrease recruitment at the population scale.

Determining the mechanism by which fish diversity influences production.

Understanding the ability of biodiversity to govern ecosystem function is essential with current pressures on natural communities from species invasions and extirpations. Changes in fish communities can be a major determinant of food web dynamics, and even small shifts in species composition or richness can translate into large effects on ecosystems. In addition, there is a large information gap in extrapolating results of small-scale biodiversity-ecosystem function experiments to natural systems with realistic environmental complexity. Thus, we tested the key mechanisms (resource complementarity and selection effect) for biodiversity to influence fish production in mesocosms and ponds. Fish diversity treatments were created by replicating species richness and species composition within each richness level. In mesocosms, increasing richness had a positive effect on fish biomass with an overyielding pattern indicating species mixtures were more productive than any individual species. Additive partitioning confirmed a positive net effect of biodiversity driven by a complementarity effect. Productivity was less affected by species diversity when species were more similar. Thus, the primary mechanism driving fish production in the mesocosms was resource complementarity. In the ponds, the mechanism driving fish production changed through time. The key mechanism was initially resource complementarity until production was influenced by the selection effect. Varying strength of intraspecific interactions resulting from differences in resource levels and heterogeneity likely caused differences in mechanisms between the mesocosm and pond experiments, as well as changes through time in the ponds. Understanding the mechanisms by which fish diversity governs ecosystem function and how environmental complexity and resource levels alter these relationships can be used to improve predictions for natural systems.

Physico-chemical properties of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) diazonium ion: a theoretical investigation.

We have explored the physico-chemical properties of NNK diazonium ion to gain insight into its shape, bonding, charge distribution, and ro-vibrational features. This information is essential if the chemical reactivity and physical properties of this important intermediate are to be understood. NNK diazonium ion is a well-known alkylating agent. Its enzymatic production, its reaction with DNA, and its role in mutagenesis/carcinogenesis have all received significant experimental study. Computational work on the ion, however, is lacking. The species is sufficiently small such that its properties may be probed using sophisticated model chemistries. We present the first in silico investigation of NNK diazonium ion. Kohn-Sham density functional theory (B3LYP/6-311G**) and coupled cluster theory (CCSD/6-31G*) were deployed to obtain energies, geometries, electrostatic potential surfaces, molecular orbitals, and vibrational analyses for several energy-minimized structures. To provide insight into the motion of NNK diazonium ion (NNKDI) in solution, molecular dynamics simulations on the solvated intermediate were undertaken. To explore the initial reactivity of this important electrophile, local Fukui indices and natural population analysis charges were predicted. Analogous ab initio work on propane diazonium ion was also performed. Our vibrational analyses suggest a relatively weak carbon-nitrogen bond and a robust nitrogen-nitrogen interaction. Our condensed Fukui indices show that the terminal nitrogen is a site of significant electrophilicity while our electrostatic predictions yield high values near the formally charged nitrogen and its α carbon.

Native fish diversity alters the effects of an invasive species on food webs.

Aquatic communities have been altered by invasive species, with impacts on native biodiversity and ecosystem function. At the same time, native biodiversity may mitigate the effects of an invader. Common carp (Cyprinus carpio) is a ubiquitous, invasive fish species that strongly influences community and ecosystem processes. We used common carp to test whether the potential effects of an invasive species are altered across a range of species diversity in native communities. In mesocosms, treatments of zero, one, three, and six native fish species were used to represent the nested subset patterns observed in fish communities of lakes in Illinois, USA. The effect of the invader was tested across fish richness treatments by adding common carp to the native community and substituting native biomass with common carp. Native species and intraspecific effects reduced invader growth. The invader reduced native fish growth; however, the negative effect was minimized with increasing native richness. The zooplankton grazer community was modified by a top-down effect from the invader that increased the amount of phytoplankton. Neither the invader nor richness treatments influenced total phosphorus or community metabolism. Overall, the invader reduced resources for native species; and the effect scaled with how the invader was incorporated into the community. Higher native diversity mitigated the impact of the invader, confirming the need to consider biodiversity when predicting the impacts of invasive species.

Cardiovascular performance of six species of field-acclimatized centrarchid sunfish during the parental care period.

Parental care is an energetically costly period of the life history of many fish species characterized by extended high intensity activity. To date, there have been no studies that have investigated the cardiovascular correlates of extended parental care in fish. Using Doppler flow probes, the cardiovascular performance of six syntopic centrarchid fish species (N=232) that provide sole, male parental care was examined across a range of water temperatures that encompass their reproductive periods (14-26 degrees C). Experiments were restricted to males but included both nesting and non-nesting individuals to evaluate the cardiovascular performance of fish during parental care. Resting values for cardiac output (Q) and heart rate (f(H)) tended to be higher for nesting fish when adjusted for variation in temperature. Both of these cardiac variables also increased with water temperature. Stroke volume (V(S)) was similar among nesting and non-nesting fish and was generally thermally insensitive. When exposed to exhaustive exercise, nesting fish took longer to exhaust than non-nesting individuals. The high resting levels found in nesting fish accompanied by only minor increases in maximal values typically resulted in reductions in cardiac scope. Cardiovascular variables recovered more quickly in nesting fish, which could facilitate the high activity and bursting associated with parental care. Interspecifically, several cardiovascular variables were correlated with parental care activity. Parental care investment became more energetically expensive as the degree of cardiac frequency modulation decreased. Additionally, as the duration of parental care increased, so did the time required for fish to become exhausted, although this relationship was probably influenced by the fact that the larger species (e.g. smallmouth bass Micropterus dolomieu; largemouth bass Micropterus salmoides) provided the lengthiest care. Collectively, these data indicate that fish that provide parental care possess adaptations, including sufficient phenotypic plasticity, such that they can enhance their ability to provide high intensity protracted care, and emphasize the nexus between behavior and physiology.

Interactions of multiple predators with different foraging modes in an aquatic food web.

Top predators can have different foraging modes that may alter their interactions and effects on food webs. Interactions between predators may be non-additive resulting from facilitation or interference, whereas their combined effects on a shared prey may result in emergent effects that are risk enhanced or risk reduced. To test the importance of multiple predators with different foraging modes, we examined the interaction between a cruising predator (largemouth bass, Micropterus salmoides) and an ambush predator (muskellunge, Esox masquinongy) foraging on a shared prey (bluegill sunfish, Lepomis macrochirus) with strong anti-predator defense behaviors. Additive and substitution designs were used to compare individual to combined predator treatments in experimental ponds. The multiple predator interaction facilitated growth of the cruising predator in the combined predator treatments, whereas predator species had substitutable effects on the growth of the ambush predator. The combined predator treatments created an emergent effect on the prey; however, the direction was dependent on the experimental design. The additive design found a risk-reducing effect, whereas the substitution design found a risk-enhancing effect for prey fish. Indirect effects from the predators weakly extended to lower trophic levels (i.e., zooplankton community). Our results highlight the need to consider differences in foraging mode of top predators, interactions between predators, and emergent effects on prey to understand food webs.

The mature larva of Poemenia albipes Cresson (Hymenoptera: Ichneumonidae, Poemeniinae) and a review of the biology of Nearctic Poemenia.

The mature larva of Poemenia albipes is figured and described, providing the first knowledge of the larval morphology of this genus. Poemenia is considered to be an ectoparasitoid on the basis of this information. The implications for the larval morphology of the Poemeniinae are discussed. The biology of Nearctic Poemenia is reviewed, with the conclusion that the genus is parasitic upon small xylophilous Apoidea that either make their tunnels or utilize those made by other insects.

Stenarella domator (Poda) [Hymenoptera: Ichneumonidae], a newly introduced species to the Nearctic, and a summary of adventive Nearctic species of Ichneumonidae.

The western Palaearctic ichneumonid Stenarella domator (Poda) is newly recorded for the Nearctic. Photographs and a new key to the genera of Nearctic Osprynchotina (Cryptinae: Cryptini) are provided. Like other species in the Osprynchotina, S. domator is an ectoparasitoid of aculeate Hymenoptera which use mud/earth in their nests. The 25 species of adventive Nearctic ichneumonids are reviewed, and the implications of their biologies for Nearctic host ranges are discussed.

First record of Nesomesochorinae (Hymenoptera: Ichneumonidae) from America north of Mexico with descriptions of two new species of Nonnus Cresson.

The subfamily Nesomesochorinae is recorded for the first time from America north of Mexico. Two new species of Nonnus (Hymenoptera: Ichneumonidae: Nesomesochorinae) are described, both from Arizona, USA and Mexico. Diagnostic characters and figures are provided to distinguish these two new species from congeners in North and Central America.

Palaeoenvironmental, epigraphic and archaeological evidence of total warfare among the Classic Maya.

Despite over a century of archaeological research, the nature and broader consequences of Maya warfare remain poorly understood. Classic period (250-950 CE) Maya warfare has largely been viewed as ritualized and limited in scope1-6. Evidence of violent warfare in the Terminal Classic period (800-950 CE) is interpreted as an escalation of military tactics that played a role in the socio-economic collapse of the Classic Maya civilization7,8. The implications of specific textual references to war events (war statements) remain unknown, however, and the paucity of field data precludes our ability to test collapse theories tied to warfare. Here we connect a massive fire event to an attack described with a Classic period war statement. Multiple lines of evidence show that a large fire occurred across the ancient city of Witzna, coincident with an epigraphic account describing an attack and burning of Witzna in 697 CE. Following this event, evidence shows a dramatic decline in human activity, indicating extensive negative impacts on the local population. These findings provide insight into strategies and broader societal impacts of Classic period warfare, clarify the war statement's meaning and show that the Maya engaged in tactics akin to total warfare earlier and more frequently than previously thought.