Selective oviposition of the mayfly Baetis bicaudatus

Abstract

Selective oviposition can have important consequences for recruitment limitation and population dynamics of organisms with complex life cycles. Temporal and spatial variation in oviposition may be driven by environmental or behavioral constraints. The goals of this study were to: (1) develop an empirical model of the substrate characteristics that best explain observed patterns of oviposition by Baetis bicaudatus (Ephemeroptera), whose females lay eggs under rocks protruding from high-elevation streams in western Colorado; and (2) test experimentally selective oviposition of mayfly females. We surveyed the number and physical characteristics of potential oviposition sites, and counted the number and density of egg masses in different streams of one watershed throughout two consecutive flight seasons. Results of surveys showed that variability in the proportion of protruding rocks with egg masses and the density of egg masses per rock were explained primarily by seasonal and annual variation in hydrology, and variation in geomorphology among streams. Moreover, surveys and experiments showed that females preferred to oviposit under relatively large rocks located in places with high splash associated with fast current, which may provide visual, mechanical or both cues to females. Experiments also showed that high densities of egg masses under certain rocks were caused by rock characteristics rather than behavioral aggregation of ovipositing females. While aggregations of egg masses provided no survival advantage, rocks selected by females had lower probabilities of desiccating during egg incubation. Our data suggest that even when protruding rocks are abundant, not all rocks are used as oviposition sites by females, due to female selectivity and to differences in rock availability within seasons, years, or streams depending on variation in climate and hydrogeomorphology. Therefore, specialized oviposition behavior combined with variation in availability of quality oviposition substrata has the potential to limit recruitment of this species.

The influence of recruitment on within-generation population dynamics of a mayfly

“…However, the study streams varied in water temperatures (average: 5.5-9.58C) and variables related to stream size (discharge: 0.091 m 3 s À1 to 2.6 m 3 s À1 ; drainage basin area: 0.05-45.9 km 2 ). In general, smaller streams have fewer large-sized emergent rocks in fast-flowing locations, which are the preferred oviposition habitats for these mayflies (Encalada and Peckarsky 2006). Streams also vary in predation risk, with brook trout (Salvelinus fontinalis Mitchell) being the only species of fish present in some streams, and others being completely fishless due to natural barriers to upstream dispersal.…”

“…Oviposition occurs from mid June to mid August depending on the year and stream (Encalada and Peckarsky 2006). Larvae hatch after 14 d (Peckarsky et al 2000), overwinter as stage I, begin to progress through later instars in April and emerge to the terrestrial adult stage from June to August.…”

“…After mating, females generally disperse upstream (Flecker and Allan 1988), oviposit one egg mass and die after oviposition (Peckarsky et al 2000). Females attach their eggs preferentially on the undersides of large rocks protruding from the water surface in relatively high current velocity locations (Encalada and Peckarsky 2006). This oviposition behavior enabled us to census egg masses and thereby to estimate recruitment of this mayfly species with high accuracy (Peckarsky et al 2000).…”

“…At each stream site we censused all egg masses oviposited under each rock protruding from the water surface. B. bicaudatus egg masses are highly conspicuous; therefore, we were able to estimate cumulative oviposition using a mapping technique (see Encalada and Peckarsky 2006 for details). Egg mass counts were made at each site five times at ;10-d intervals over the flight period of Baetis.…”

“…In spite of many parallels between the complexity of the life cycles of stream insects and marine invertebrates (Elliott et al 1988, Palmer et al 1996, Downes and Keough 1998, there have been very few studies addressing the supply of new recruits to streams (Bunn and Hughes 1997, Peckarsky et al 2000, Encalada and Peckarsky 2006 and their relationship with subsequent patterns of larval abundance (but see Hildrew et al 2004, Reich and Downes 2004, Lancaster et al 2010. Most studies of stream invertebrate populations have focused on the effects of postrecruitment processes, such as biotic interactions (competition, predation) (Kohler 1984, Kerans et al 1995, environmental disturbance Feifarek 1994, Lytle 2000) and fluid mediated movement (Forrester 1994, Fonseca and Hart 1996.…”