Effects of Developmental Acclimation on Adult Salinity Tolerance in the Freshwater‐Invading Copepod Eurytemora affinis

Abstract

Invasive species are commonly thought to have broad tolerances that enable them to colonize new habitats, but this assumption has rarely been tested. In particular, the relative importance of acclimation (plasticity) and adaptation for invasion success are poorly understood. This study examined effects of short-term and developmental acclimation on adult salinity tolerance in the copepod Eurytemora affinis. This microcrustacean occurs in estuarine and salt marsh habitats but has invaded freshwater habitats within the past century. Effects of short-term acclimation were determined by comparing adult survival in response to acute versus gradual salinity change to low salinity (fresh water). Effects of developmental acclimation on adult tolerance were determined using a split-brood 4 x 2 factorial experimental design for one brackish-water population from Edgartown Great Pond, Massachusetts. Twenty full-sib clutches were split and reared at four salinities (fresh, 5, 10, and 27 practical salinity units [PSU]). On reaching adulthood, clutches from three of the salinity treatments (no survivors at fresh) were split into low- (fresh) and high- (40 PSU) salinity stress treatments, at which survival was measured for 24 h. Short-term acclimation of adults did not appear to have a long-term affect on low-salinity tolerance, given that gradual transfers to fresh water enhanced survival relative to acute transfers in the short term (after 7 h) but not over a longer period of 8 d. Developmental acclimation had contrasting effects on low- versus high-salinity tolerance. Namely, rearing salinity had a significant effect on tolerance of high-salinity (40 PSU) stress but no significant effect on tolerance of low-salinity (freshwater) stress. In addition, there was a significant effect of clutch on survival under freshwater conditions, indicating a genetic component to low-salinity tolerance but no significant clutch effect in response to high salinity. While developmental acclimation might enhance survival at higher salinities, the minimal effect of acclimation and significant effect of clutch on low-salinity tolerance suggest the importance of natural selection during freshwater invasion events.

Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata)

“…One relates to the species showing some important pre-adaptation in life-history or stress tolerance traits (Thebaud et al 1996, Reichard & Hamilton 1997, Kolar and Lodge 2001, Sakai et al 2001), for instance due to adaptations to large seasonal disturbances in their native range (Winkler et al 2008). Another reason is high evolvability or plasticity in life-history or stress tolerance traits (Lee andPetersen 2003, Lee et al 2003). Yet another reason is lack of parasites or predators in the invaded environment (Sax et al 2005).…”

Calanipeda aquaedulcis and Arctodiaptomus salinus are exceptionally euryhaline osmoconformers: evidence from mortality, oxygen consumption, and mass density patterns

“…Copepod mortality (M, %) was calculated as: M = 100 D / (D + s), where D is the number of dead individuals, and s is the number of surviving individuals. The salinity tolerance range in Calanipeda aquaedulcis and Arctodiaptomus salinus was estimated taking into account the lethal salinity values affecting 50% of the original number (LS 50 ) (Hopper 1960, Parra et al 2005, Chen et al 2006) in 5 to 10 d. We chose this period because the process of salinity acclimation in crustaceans usually takes at least 3 d (Lance 1963, Khlebovich 1981, Lee & Petersen 2003.…”

“…For comparison, Pseudodiaptomus annandalei from a lagoon near Wukan Bay tolerated gradual salinity increases from 22 to 35 psu and decreases from 22 to 5 psu (Chen et al 2006). Acartia tonsa (Lance 1963, Cervetto et al 1999, Hubareva et al 2008 and Eurytemora affinis (Lee & Petersen 2003) successfully survived gradual salinity changes over 20 psu under experimental conditions.…”

Molecular characterization and mRNA expression of grp78 and hsp90A in the estuarine copepod Eurytemora affinis

“…Capacity of aquatic organisms to tolerate those environmental variations determines their spatio-temporal repartition along the estuarine gradient and their capacity to survive and to overlap low tolerant-species in such a stressful environment (Laprise and Dodson 1994). The calanoid copepod Eurytemora affinis is known to have physiological capacities to invade freshwater environment through the saline gradient of estuaries (Lee 1999;Lee and Peterson 2003). As a result, this species is distributed in a large spectrum of habitats characterized by large range of salinity, from hyperhaline salt marches to lakes and is one of the most common copepods of the northern hemisphere estuaries (Lee 1999).…”