Bart T. De Stasio

The Seed Bank of a Freshwater Crustacean: Copepodology for the Plant Ecologist

The spatial and temporal aspects of dormancy in a freshwater copepod, Diaptomus sanguineus, were investigated during three consecutive years in Bullhead Pond, Rhode Island. Patterns of diapausing egg production and deposition were monitored with plankton sampling and settling traps. Vertical and horizontal distributions of diapausing eggs in sediments were investigated by taking core samples. Diapausing eggs removed from sediments were tested in the laboratory for hatching ability. The long—term spatial and temporal patterns of emergence from the diapausing egg stage were documented in the field using inverted plastic funnel traps sampled weekly. The field data along with an estimated annual budget for diapausing eggs in the pond suggest that D. sanguineus has an egg bank, analogous to the seed banks of plants, that allows it to survive through harsh environmental periods. See full-text article at JSTOR

Rate of evolution slowed by a dormant propagule pool

Theoretical models of plant seed banks and common sense suggest that stores of dormant propagules must slow down the rate of genetic change1,2 because they sequester a substantial fraction of the gene pool from the influence of microevolutionary processes in each generation. The magnitude of the effect must represent a balance between the extent of selection and the fraction of the dormant pool that returns to the active population in each generation (and the other microevolutionary processes of migration, drift and mutation). For most populations, in which to observe the action of selection is difficult in itself, detecting the added influence of a dormant propagule pool will be more difficult still. Here we report the effect of hatching of diapausing eggs from lake sediments on the rate of phenotypic change in two populations of the freshwater copepod, Diaptomus sanguineus. When the input of new eggs to the sediments was eliminated by a brief but intense two-year appearance of predators, the role of dormant stages in slowing evolution was clearly seen.

Diapause in Aquatic Invertebrates Theory and Human Use

PART I: Strategies and Mechanisms of Diapause in Aquatic Invertebrates 1. INTRODUCTION TO DIAPAUSE, Victor R. Alekseev, Oscar Ravera & Bart T. De Stasio 1. Diagnosis of diapause, 1.2 Ecological causes of diapause in aquatic organisms, 1.3 Terminology on dormancy 2. TIMING OF DIAPAUSE IN MONOGONONT ROTIFERS: MECHANISMS AND STRATEGIES, John J. Gilbert 2.1 Introduction, 2.2 Female types and the fertilized resting egg, 2.3 The timing of sex: environmental controls, 2.4 The Timing of sex: endogenous controls, 2.5 General mechanistic models for the control of mixis, 2.6 Theoretical models for maximizing resting-egg production, 2.7 Diapausing parthenogenetic eggs, 2.8 Acknowledgments 3. DIAPAUSE IN CRUSTACEANS: Peculiarities of Induction, Victor R. Alekseev 3.1 Introduction, 3.2 Diapause in crustacean life cycles, 3.3 Presence of diapause among crustaceans, 3.4 Evolution of points of view on inducing factors, 3.5 Diapause as a photoperiodic response, 3.6 Light as the source of information about the season, 3.7 Role of temperature and photoperiod in diapause induction, 3.8 Population density and manifestations of photoperiodic reactions, 3.9 Food quality and diapause induction in Crustacea, 3.10 Population polymorphism and inheritance of photoperiodic responses, 3.11 Heredity of photoperiodic responses, 3.12 Acknowledgments 4. REACTIVATION OF DIAPAUSING CRUSTACEANS, Victor R. Alekseev 4.1 Introduction, 4.2 Patterns of reactivation processes for different types of diapause, 4.3 Endogenous phase of diapause, 4.4 Reactivation action of oxygen, 4.5 Participation of carbon dioxide in reactivation, 4.6 Hormonal basis of diapause, 4.7 Acknowledgments 5. DIAPAUSE IN AQUATIC INSECTS, WITH EMPHASIS ON MOSQUITOES, Elena B. Vinogradova 5.1 Introduction, 5.2Mosquitoes (Culicidae), 5.3 Other groups of aquatic insects, 5.4 Acknowledgments 6. A BRIEF PERSPECTIVE ON MOLECULAR MECHANISMS OF DIAPAUSE IN AQUATIC INVERTEBRATES, Victor R. Alekseev 6.1 Introduction, 6.2. Molecular mechanism of diapause in nematode Caenorhabditis elegans, 6.3 Acknowledgments PART 2: The Role of Diapause in Science and Human Uses 7. EGG BANK FORMATION BY AQUATIC INVERTEBRATES: A BRIDGE ACROSS DISCIPLINARY BOUNDARIES, Bart T. De Stasio 7.1 Introduction, 7.2 Dormancy processes, 7.3 Egg bank size and dynamics, 7.4 Creating an egg bank, 7.5 Conclusion, 7.6 Acknowledgements 8. USE OF CLADOCERAN RESTING EGGS TO TRACE CLIMATE-DRIVEN AND ANTHROPOGENIC CHANGES IN AQUATIC ECOSYSTEMS, Susanne L. Amsinck, Erik Jeppesen & Dirk Verschuren 8.1 Introduction, 8.2 Tracing acidification, 8.3 Tracing eutrophication, 8.4 Tracing fish introductions and biomanipulation, 8.5 Tracing heavy metal pollution, 8.6 Tracing climate change, 8.7 Discussion and conclusion: limitations, concerns and future potentials, 8.8 Acknowledgements 9. RECONSTRUCTING MICRO-EVOLUTIONARY DYNAMICS FROM LAYERED EGG BANKS, Luc De Meester, Joachim Mergeay, Helen Michels & Ellen Decaestecker 9.1 Introduction: dormant stages and the study of micro-evolution, 9.2 A short survey of recent success stories, 9.3 Pitfalls, 9.4 Conclusion and future directions, 9.5 Acknowledgments 10. DOES TIMING OF EMERGENCE WITHIN A SEASON AFFECT THE EVOLUTION OF POST-DIAPAUSE TRAITS? Post-diapause and directly developing phenotypes of Daphnia, Kestutis Arbaciauskas 10.1 Introduction, 10.2 Daphnia life cycle, 10.3 Neonates: biochemical quality and body size, 10.4 Physiology: respiration and starvation resistance, 10.5 Life-history: growth, allocation and relative fitness, 10.6 Descendents of post-diapause and d

A Field Test for the Cues of Disapause in a Freshwater Copepod

The freshwater calanoid copepod Diaptomus sanguineus switches each year in spring from making eggs that hatch immediately to making diapausing eggs that rest in lake sediments for an extended period. In lakes and ponds containing planktivorous fish, the timing of the switch is highly consistent between years and comes at the theoretically optimal time (late March) to avoid intense summer predation. In fishless ponds the timing comes 1—2 mo later. We investigate here the environmental cues used by the copepods to time the switch to diapause. Through the use of both field and laboratory manipulations, we show that temperature and photoperiod play central roles as diapause stimuli. A field manipulation of fish density failed to reveal either a direct induction of diapause or any more subtle effects of fish occurrence on diapause timing. The copepods made immediately hatching eggs under short—day or low—temperature conditions, and diapausing eggs under long days or high temperatures. There appears to be variation between individuals in their responses to temperature and photoperiod so that similar diapause phenologies are produced by different sensitivities to the environmental cues.

Environmental variability and the persistence of multiple emergence strategies

Studies of plant and animal populations have demonstrated the occurrence of multiple and mixed life history strategies such as polymodal timing of germination and emergence from dormancy. We present the results of a simulation model used to test whether between-year variance in mortality can lead to the persistence of multiple hatching strategies considered over an ecological time scale (50 years). The model is based on the general life history characteristics of a population of planktonic copepods (Diaptomus sanguineus) in Bullhead Pond, Rhode Island. Our model results demonstrate that, given a range of between-year variance in mortality, multiple strategies for timing of emergence can persist in a common environment for ecologically relevant periods of time. A qualitative test of the model comparing field estimates of mean and variance of mortality in Bullhead Pond with the region of persistence indicates that the model results are in approximate agreement with field estimates. The results suggest that variability in year-to-year selection pressures, such as predation or harsh winters, may play an important role in determining the evolution of life histories.

Egg Bank Formation by Aquatic Invertebrates: A Bridge Across Disciplinary Boundaries

Aquatic organisms live in variable environments. Changes in factors that affect survival and reproduction of individuals occur on various temporal and spatial scales, and can have both shortand long-term consequences (e.g. Brendonck et al. 1998). One life history adaptation to lessen the impact of such variability is to undergo dormancy, a period of suppressed development, during part of a lifetime (Tauber et al. 1986; Danks 1987; Hairston 1998). Similar to the seed banks of plants, the accumulation of dormant invertebrates in the aquatic environment has been termed the “egg bank” of the organism, or more generally, a biotic reservoir (De Stasio 1989; Hairston 1996; Brendonck & De Meester 2003). When dormancy persists over multiple seasons or generations, the egg bank is considered a mixed persistent egg bank, whereas shorter durations of dormancy result in transient egg banks that may persist less than a single year (Brendonck & De Meester 2003). Contributions of individuals from the egg bank to the active population will vary depending on local conditions and dynamics. Typically, only the top few centimeters of sediment contain individuals that hatch and contribute to the active population. This zone has been labeled the active egg bank (Cáceres & Hairston 1998), and the factors that determine the depth of the active egg bank can be important features of ecosystems. Recent extensive reviews (Brendonck & De Meester 2003; Gyllström & Hansson 2004) provide comprehensive overviews of the structure and dynamics of egg banks of freshwater organisms. This chapter provides an update of those reviews with respect to egg bank formation, and also includes information on egg banks in marine systems. As one of the common features of all aquatic environments, the study of egg banks provides a bridge across disciplinary boundaries and encourages a focus on processes that apply to all habitats.

Coral Growth Assessment on an Established Artificial Reef in Antigua

Anthropogenic pressure on coral reef ecosystems has increased the need for effective restoration and rehabilitation as a management tool. However, quantifying the success of restoration projects can be difficult, and adequate monitoring data are scarce. This study compared growth rates over a six-year period of three Caribbean coral species, staghorn coral (Acropora cervicornis), elkhorn coral (Acropora palmata), and thick finger coral (Porites porites), transplanted on an artificial reef off Maiden Island, Antigua, to literature values for the same species growing on naturally formed reefs in the Caribbean region. The average growth rate of staghorn coral was considerably lower than growth rates reported in the literature, while elkhorn and finger corals showed growth rates similar to literature values. The observed inter- and intraspecific differences may be caused by species-specific growth requirements and/or restoration site conditions, factors that should be taken into account when planning future projects involving coral transplant or rescue. This study also determined the analytical precision of a ‘low tech’ monitoring method using a basic underwater digital camera and the software program ImageJ to measure growth rates of corals. Measurement error between volunteer analysts receiving only minimal training was shown to be very small, ranging from 0.37–1.40% depending on the coral species. This confirms the validity of this basic technique, particularly in cases where data are sparse and resources for monitoring are extremely limited.

Dreissenid driving tests: going the “wrong” way in Green Bay, Lake Michigan?

Numero us studies o f the Laurentian Great Lakes have shown decreases in Chlorophyll-a (Chl-a) and phytoplankton abundance following invasion by the zebra mussel Dreissena po/ymorpha (LAVRENTYEV et al. 1995, IDRISI et al. 2001, BARBIERO et al. 2006, DEPEW et al. 2006). Zebra mussels filter large volumes of water and have the capacity to clear water of a wide range of particles. The largest embayment o f Lake Michigan is Green Bay, o ne o f the most productive ecosystems in the Laurentian Great Lakes. Extensive studies prior to invasion of the bay in 1992 by zebra mussels documented a large effect o f nutrient inflows from the Fox River, leading to a strong trophic gradient in the lower bay (RICHMAN et al. 1984, SAGER & RICHMAN 1991, DE STASIO & RICHMAN 1998). Early modeling studies predicted that zebra mussel filtering would lead to significant decreases in phytoplankton in the bay, especially in the well-mixed lower bay (PADILLA et al. 1996). Anecdotal observations did not support these predictions following the invasion, and here we document actual changes by determining average summer abundances of Chl-a and phytoplankton following the invasion of Green Bay by Dreissena polymorpha.