Hatching phenology, life history and egg bank size of fairy shrimp Branchipodopsis spp. (Branchiopoda, Crustacea) in relation to the ephemerality of their rock pool habitat

Abstract

In temporary aquatic habitats, permanence and the severe disturbance associated with desiccation are strong selective agents expected to lead to differentiation in life history strategies in populations experiencing different disturbance regimes. Besides optimal timing of hatching of dormant life stages, maturation and reproduction, pool inhabitants also benefit from the acquisition of reliable cues for the quality of the ambient environment. We investigated whether hatching patterns, life history characteristics and egg bank size of Branchipodopsis fairy shrimp (Branchiopoda, Anostraca) inhabiting a cluster of temporary rock pools in South Africa reflect variation in habitat stability and hatching cues. Long-term hydrological variation was used to select pools along a gradient of habitat stability. Initial conductivity was a good indicator for the length of inundations. No hatching occurred under elevated conductivities, which may present a mechanism to avoid abortive hatching. Egg bank size was unaffected by habitat size or habitat stability but instead was related to cover by a protective sheet of dry aquatic vegetation, which presumably counteracts egg bank erosion by wind when pools are dry. Life history but not hatching phenology reflected some aspects of habitat stability. Fairy shrimp populations in ephemeral pools started reproduction earlier than populations in more stable habitats. Additional common garden or transplant experiments, however, will be required to assess the relative importance of environmental and genetic components in explaining the observed variation and acquire more insight into the trade-offs that lie at the base of the evolution of life history strategies along the pond permanence gradient.

Long‐term effects of salinity and disturbance regime on active and dormant crustacean communities

“…This experiment is a follow-up of a previous study in which the effect of salinity on the succession of permanent inhabitants of temporary wetlands was assessed during only one inundation cycle (Waterkeyn et al 2010). …”

“…However, for this to be a successful survival strategy, species need to hatch fractionally corresponding with chances for successful recruitment (Cohen 1966;Brown and Venable 1986), grow in time to maturity, and produce sufficient numbers of dormant eggs to replenish the dormant egg bank to compensate for losses due to hatching and mortality. Under more saline conditions, freshwater organisms are unlikely to hatch optimally and to survive until reproduction (Nielsen and Brock 2009;Vanschoenwinkel et al 2010). Failure to reproduce (abortive hatching) during several consecutive seasons may cause depletion of the dormant egg bank and eventually extinction of the local populations.…”

“…Since modified hydroregimes and salinities often go along with changes in other wetland characteristics, such as water quality, turbidity, or vegetation structure, or with biotic pressure by adding or removing species (Wellborn et al 1996;Nielsen et al 2003a;, there may also be second-order effects. Even more, entire regime shifts (Scheffer et al 1993) can be triggered by the salinitymediated presence or absence of keystone species (Jeppesen et al 2007;Waterkeyn et al 2010).…”

“…Because of their shallow depth and small volume, Mediterranean temporary wetlands in general are poorly buffered against changes in hydrology and are thus exceptionally susceptible to climate change, whose adverse effects may aggravate the effect of other anthropogenic stressors, such as destruction or change of the original habitat, pollution, irrigation, and drainage (EPCN 2008). Several field surveys already demonstrated that both salinity and hydroregime (also indicated as ''disturbance regime'' because of recurring drought acting as a disturbance; Wellborn et al 1996;Vanschoenwinkel et al 2010) are the most important factors shaping plant and invertebrate communities and influencing diversity in Mediterranean temporary wetlands (Boix et al 2008;Waterkeyn et al 2008). Hydrological modifications and changes in salinity therefore constitute important threats to the unique biodiversity supported by this priority habitat for conservation (Habitat Directive, Natura code 3170, 92/43/CEE, 21 May 1992) (Zacharias et al 2007).…”

Modes, mechanisms and evidence of bet hedging in rotifer diapause traits

“…In both cases, the level of empirical evidence met Category II b . Studies of anostracans typically dealt with the timing of diapausing egg hatching and were most prevalent in Category III (Hildrew, 1985;Saiah & Perrin, 1990;Simovich & Hathaway, 1997;Dumont & Ali, 2004;Vanschoenwinkel et al, 2010), with a remarkable exception in Branchinecta sandiegonensis Fugate, 1993, for which hatching fractions in different populations were found to be optimal given their respective frequency patterns of pool filling, so that Category VI was reached (Philipi et al, 2001). Similarly in copepods, it has been found that the timing of diapausing egg production in Diaptomus sanguineus Forbes, 1876, is in close agreement with a simulation-derived evolutionary stable strategy, thus reaching the highest level of empirical evidence for a conservative bethedging trait (Category VI).…”