Cyst Distribution and Hatching Pattern ofChirocephalus ruffoi (Crustacea, Anostraca) in an Experimental Undisturbed Pool

Abstract

The pattern of cyst distribution in the absence of turbation and their hatching behaviour were studied in an outdoor artificial pool, where just differentiated adults of the anostracan Chirocephalus ruffoi (sex ratio 1:3) lived until it dried up. The horizontal and vertical distributions of cysts in the pool bed were determined. The comparison between cyst bank estimate (MURA, 2004) and the actual number of cysts counted in the pool bed revealed an estimate error of 20.9%. Resting eggs occurred only in the upper 2.5 cm thick soil sections and decreased within this section as depth increased. Peripheral areas of the pool contained significantly larger numbers of cysts than the central area. Multiway analysis on the results recorded in hatching success (nested ANOVA) revealed that the differences were significantly affected by initial soil conditions, treatment and vertical distribution of cysts. Among these factors, vertical distribution (sections nested in cores) was the most influential. Hatching success was significantly inversely related to depth. Differences in the timing of hatching depending on the above considered factors were also noted. A nearly synchronous hatching pattern was observed only for cysts from initially dry sediment of the uppermost layers. In all successively deeper layers, hatching showed multiple peaks and was increasingly delayed and erratic (already mentioned). ANCOVA within each of the experimental conditions revealed significant differences in hatching frequencies (time as covariate) depending on sediment depth. Within any given layer, ANCOVA revealed a significant influence of initial sediment conditions and treatment on the timing of hatching. IntroductionPersistence in highly variable habitats such as those inhabited by the fairy shrimp, requires adaptations both in the reproductive characteristics of active populations and in the hatching behaviour of their resting stages (BELK and COLE, 1975;WIGGINS et al., 1980;WILLIAMS, 1985). One of the most conspicuous aspects of such adaptations is the fact that not all of the eggs deposited during active life, even within a single cohort, hatch during subsequent inundations. This leads to the formation of an egg bank in pool beds which buffers the risk of extinction of the population.The behaviour of an egg bank is thus of great importance for the persistence of a given species in highly variable habitats. In spite of this, and in contrast to the plethora of studies on the cyst banks of zooplankters from permanent waterbodies (see review in MARCUS, 1996;MURA, 2004), no information on the structure and functioning of anostracan cyst banks was available until recent years.The function of egg banks (sensu DE STASIO, 1989) is especially important in regions where the climate is extremely unpredictable, and this was recently investigated in two studies aimed specifically at evaluating the size and dynamics of the egg banks of the anostracan Branchipodopsis wolfi inhabiting some short lived desert rock-pools in Botswana Internat. Rev. Hyd...

How do freshwater organisms cross the “dry ocean”? A review on passive dispersal and colonization processes with a special focus on temporary ponds

“…Thiéry, 1997;Brendonck et al, 1998;Mura, 2004Mura, , 2005 and the role of the wind in the dispersal of zooplankton, large branchiopods eggs and other invertebrates (Baujard & Martiny, 1994;Cáceres & Soluk, 2002;Graham & Wirth, 2008 and literature therein). As already reported for phytoplankton, the effectiveness of the dispersal of these animals seems to be linked to the distance among sites.…”

Dispersal of large branchiopod cysts: potential movement by wind from potholes on the Colorado Plateau

“…Cyst numbers collected in the filters were a function of the amount of sediment pulled off the pothole sediment surface, but the relationship was not as strong as expected. This variation could be due to differences in the concentration of cysts in different parts of the pothole, which results from differential deposition of cysts (Khalaf & Hall, 1975;Mura, 2005;Hulsmans et al, 2006) and re-working of cysts and sediment by wind (Eriksen et al, 1986;Thiery, 1998). Another source of variation is the volume of sediment moved by wind.…”

“…Enough rain to saturate the sediment and leave standing water will stimulate hatching of a fraction of cysts in the sediment (Hildrew, 1985;Brendonck & De Meester, 2003;Mura, 2004Mura, , 2005, but if the water evaporates before maturation and reproduction, the sediment cyst bank is depleted. During extended droughts, rain events are more sporadic, and often less water falls per event (Table 4).…”

Observations on the hatching dynamics and phenology of co-occurring large branchiopods from a small temporary pool in western India usingex situsediment rehydration

“…Dry sediments (upper 2 cm; see Brendonck and De Meester, 2003;Mura, 2005) were scraped off using a clean garden spade from the centre as well as the sides of the pool after the pool had been dry for about a month. Approximately 0.5 kg of sediment was collected at a time.…”