Mating success and its consequences for population growth in an estuarine copepod

Abstract

We conducted experiments on mating success of the estuarine copepod Eurytemora affinis in the San Francisco Estuary, USA. The experimental approach was to isolate virgin pairs (one male and one female) in containers varying in volume from 0.03 to 32 l for 2, 4, or 8 h. Mating was considered successful if viable eggs were produced by individual females subsequently incubated for up to 5 d. The experimental data were analyzed by fitting a 3-parameter model to the data to determine the volume search rate of males. Mating frequencies indicated a volume search rate for E. affinis males of 7.2 ± 4.0 l h -1 (172 ± 96 l d -1, 95% CL), about 20-fold higher than that for Acartia hudsonica previously determined by a similar method. A simple population model showed that the critical population density needed to maintain the E. affinis population can be well below the seasonally low abundance of this copepod in the San Francisco Estuary. The low critical density may allow population persistence in an estuary without the production of resting eggs. KEY WORDS: Copepod mating · Allee effects · Population growth · Volume search rate Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 377: [183][184][185][186][187][188][189][190][191] 2009 (Katona 1973, Griffiths & Frost 1976, van Leeuwen & Maly 1991, Yen et al. 1998. Increasing detection range increases the volume search rate, i.e. the volume searched by males for females per unit time (Kiørboe 2007), which, in turn, reduces the population density needed to prevent mate limitation (Choi & Kimmerer 2008).In the present study, we determined the volume search rate for males of the calanoid copepod Eurytemora affinis and assessed the consequences of this rate for population recovery from low abundance. E. affinis (~1 mm total length) is a dominant species in many temperate estuaries, usually inhabiting lowsalinity areas, and is often associated with the maximum turbidity zone (e.g. Hough & Naylor 1991, Peitsch et al. 2000, David et al. 2005). The copepod is also an important food source for macrozooplankton such as mysids and many estuarine-dependent fishes such as striped bass Morone saxatilis (Burkill & Kendall 1982, Meng & Orsi 1991, Thorp & Casper 2003. E. affinis is capable of producing resting eggs in response to environmental conditions such as temperature, photoperiod, and crowding (Ban & Minoda 1992, Ban 1992. Mating behavior and fertilization have been well documented (Heinle 1970, Katona 1973, Katona 1975. Mate finding in E. affinis is asymmetric in that the female produces a pheromone signal and searches primarily for food, whereas the male detects the pheromone and pursues the female (Katona 1973). It is not well understood, however, how this mating behavior relates to population growth (Kiørboe 2007) and, in particular, how dilute the population can become before it is unable to recover.In the San Francisco Estuary, Eurytemora affinis has historically been abundant and reproductively active throughout the year i...

Predation risk suppresses mating success and offspring production in the coastal marine copepod, Eurytemora herdmani

“…Recent copepod-population growth models suggest that small population densities (Choi andKimmerer 2008, 2009) and biased sex ratios (Kiørboe 2007(Kiørboe , 2008 decrease copepod mating success and subsequent population growth by reducing mate-encounter rates (Kiørboe and Bagøien 2005;Visser and Kiørboe 2006;Kramer et al 2011). Here, we show in small (20-mL) vessels, where encounter rates are not limiting, that E. herdmani mating success is significantly reduced by the presence of a predator cue.…”

“…Trials were conducted in small volumes (20 mL) to facilitate high encounter rates and because this volume is comparable to volumes that yielded maximum mating success in a previous study on the congeneric Eurytemora affinis (Choi and Kimmerer 2009). A consumptive predator treatment (predator present), nonconsumptive predator treatments (physical predator mimic, chemical predator cue, combined physical + chemical predator cue) and a control (predator absent) were randomly assigned to containers (n 5 30 per treatment) and copepods were randomly assigned to each treatment.…”

“…Traditionally, population growth experiments have centered on the effects that environmental factors such as temperature and food concentration have on copepod egg production rate (Checkley 1980;Huntley and Lopez 1992;Mauchline 1998). However, more recent theoretical and experimental studies indicate that demographic factors, such as population density and sex ratio, also strongly affect population growth rates for copepods (Choi and Kimmerer 2008;Kiørboe 2008;Kramer et al 2008).…”

“…However, these field surveys primarily assessed the consumptive effects of predators on copepod prey, in terms of reducing population size (Ohman 1986;Hirst and Kiørboe 2002) or skewing copepod sex ratio (Hirst et al 2010). Recent studies indicate that changes in copepod sex ratio and density can decrease mate-encounter rates and, thus, successful mating events (Choi andKimmerer 2008, 2009;Kiørboe 2008). However, the potential for predators to affect copepod-mating behavior via nonconsumptive effects and, thus, alter subsequent population growth, has received little attention.…”

Spermatophore production as a function of food abundance and age in the calanoid copepods, Acartia tonsa and Acartia hudsonica

“…Once mature, males were randomly placed individual into 60 × 30 mm Petri dishes filled with ~30 mL of >700 μg C L −1 (food-replete) or ~200 μg C L −1 (food-limited) food solutions (Besiktepe and Dam 2002), or filtered sea water (no-food treatment). Choi and Kimmerer (2009) have shown that this small volume of water does not affect mating in Acartia sp. The food solutions consisted of 0.2-μm filtered sea water to which T. weissflogii and Tetraselmis sp.…”