J. Curtis Creighton

Habitat enhancement and native fish conservation: can enhancement of channel complexity promote the coexistence of native and introduced fishes?

Native fishes worldwide have declined as a consequence of habitat loss and degradation and introduction of non-native species. In response to these declines, river restoration projects have been initiated to enhance habitat and remove introduced fishes; however, non-native fish removal is not always logistically feasible or socially acceptable. Consequently, managers often seek to enhance degraded habitat in such a way that native fishes can coexist with introduced species. We quantified dynamics of fish communities to three newly constructed side channels in the Provo River, Utah, USA, to determine if and how they promoted coexistence between native fishes (nine species) and non-native brown trout (Salmo trutta L.). Native and introduced fishes responded differently in each side channel as a function of the unique characteristics and histories of side channels. Beaver activity in two of the three side channels caused habitat differentiation or channel isolation that facilitated the establishment of native species. The third side channel had greater connectivity to and similar habitat as the main channel of the Provo River, resulting in a similar fish community to main channel habitats (i.e. dominated by brown trout with only a few native fish species). These results demonstrate the importance of understanding habitat preferences for each species in a community to guide habitat enhancement projects and the need to create refuge habitats for native fishes.

Residency Time as an Indicator of Reproductive Restraint in Male Burying Beetles

The cost of reproduction theory posits that there are trade-offs between current and future reproduction because resources that are allocated to current offspring cannot be used for future reproductive opportunities. Two adaptive reproductive strategies have been hypothesized to offset the costs of reproduction and maximize lifetime fitness. The terminal investment hypothesis predicts that as individuals age they will allocate more resources to current reproduction as a response to decreasing residual reproductive value. The reproductive restraint hypotheses predicts that as individuals age they will allocate fewer resources to current reproduction to increase the chance of surviving for an additional reproductive opportunity. In this study, we test for adaptive responses to advancing age in male burying beetles, Nicrophorus orbicollis. Burying beetles use facultative biparental care, but the male typically abandons the brood before the female. Previous work in male burying beetles has suggested several factors to explain variation in male residency time, but no study has observed male behavior throughout their entire reproductive lifetimes to determine whether males change residency time in an adaptive way with age. We compared residency time of males that reproduced biparentally, uniparentally, and on different-sized carcasses to determine if they used an adaptive reproductive strategy. Males did not increase residency time as they aged when reproducing biparentally, but decreased residency time with age when reproducing uniparentally. A decrease in parental care with age is consistent with a reproductive restraint strategy. When female age increased over time, males did not increase their residency time to compensate for deteriorating female condition. To our knowledge, this is the first test of adaptive reproductive allocation strategies in male burying beetles.

Differences in Patterns of Reproductive Allocation between the Sexes in Nicrophorus orbicollis.

Organisms are selected to maximize lifetime reproductive success by balancing the costs of current reproduction with costs to future survival and fecundity. Males and females typically face different reproductive costs, which makes comparisons of their reproductive strategies difficult. Burying beetles provide a unique system that allows us to compare the costs of reproduction between the sexes because males and females are capable of raising offspring together or alone and carcass preparation and offspring care represent the majority of reproductive costs for both sexes. Because both sexes perform the same functions of carcass preparation and offspring care, we predict that they would experience similar costs and have similar life history patterns. In this study we assess the cost of reproduction in male Nicrophorus orbicollis and compare to patterns observed in females. We compare the reproductive strategies of single males and females that provided pre- and post-hatching parental care. There is a cost to reproduction for both males and females, but the sexes respond to these costs differently. Females match brood size with carcass size, and thus maximize the lifetime number of offspring on a given size carcass. Males cull proportionately more offspring on all carcass sizes, and thus have a lower lifetime number of offspring compared to females. Females exhibit an adaptive reproductive strategy based on resource availability, but male reproductive strategies are not adaptive in relation to resource availability.

A multivariate approach to the analysis of within lifetime variation in life history

Summary Ecological and environmental gradients create varying selective pressures on organisms that result in differences in optimal life history tactics. Moreover, life histories are inherently multivariate, consisting of a coordinated suite of life history traits that vary over an organisms lifetime. Such variation can be described as a trajectory of phenotypic change through time in multivariate space defined by a set of life history traits. We demonstrate the use of phenotypic trajectory analysis as a multivariate analytical approach for quantifying and comparing phenotypic change in life history throughout an organisms life. Life history trajectories have attributes – magnitude, direction, and shape – that can be quantified and statistically compared. We demonstrate the construction of trajectories using levels characterized by individuals with the same age or similar state, and we show how this approach can be used to evaluate the evolution of life history strategies given predictions from life history theory. We demonstrate the utility of phenotypic trajectory analysis for life histories using two examples. We compare life history trajectories of burying beetles and show that females balance costs of reproduction differently based on resource availability. We also characterize life history trajectories of livebearing fish in different predation environments. We show that females in non-predator environments, but not predator environments, exhibit trajectories consistent with the terminal investment hypothesis. While analysing life history variation in a multivariate framework is not novel, we show that phenotypic trajectory analysis provides a method to statistically test age- and state-based predictions of life history theory.

Why does it take two to tango? Lifetime fitness consequences of parental care in a burying beetle

In species that require parental care, each parent can either care for their offspring or leave them in the care of the other parent. For each parent this creates three possible parental care strategies: biparental care, uniparental (male or female) care, and uniparental desertion by either the male or female. The burying beetle, Nicrophorus orbicollis, typically exhibits biparental care of offspring, and thus provides a unique system that allows us to compare the fitness benefits of these parental care strategies in an unconfounded way. In this study, we assess the lifetime fitness of biparental care, uniparental care, and uniparental desertion strategies in both male and female N. orbicollis. Specifically, we tested for increased fitness of the biparental care strategy compared to uniparental care strategies. Second, we test for equality of fitness between uniparental care and uniparental desertion strategies. Surprisingly, biparental care yields lower lifetime fitness for both parents compared to the other two strategies. Also, uniparental care and uniparental desertion strategies yielded equal fitness. The evolution of biparental care in this system is not consistent with the expectation of a mutual fitness benefit. We discuss other potential explanations for the evolution of biparental care in this system.

A good day to die: bridging the gap between costs and benefits of parental care

In species that provide parental care, offspring survival is often completely dependent on protection and resources afforded by the parents. Therefore, parents gain no fitness unless they raise offspring to a critical point of independence. In these species, selection should shape parental life history to increase their chances of surviving to this critical point. We test this hypothesis using females of two species of burying beetles, Nicrophorus orbicollis and N. marginatus. Burying beetles breed on small, vertebrate carcasses, and reproduction can be divided into two stages: carcass preparation and larva provisioning. Females were allowed to reproduce repeatedly until they died, and the stage in which each female died was recorded. Most females died while waiting for another carcass for their next reproductive bout or during carcass preparation, which indicates that females may have a physiological mechanism that allows them to delay death until their final brood is independent of parental care.Significance statementIn this paper, we show that female burying beetles of two species do not die at random times during reproduction, but instead die after they have finished caring for their offspring. This is the first time that non-random death has been shown in burying beetles. We show that females that die after offspring care is complete have a higher fitness than females that die at random because offspring in many species of burying beetles depend on parental care for food provisioning and protection. We also propose a hormonal mechanism through which females might extend their lives to allow them to finish caring for their offspring.