Nature and nurture in dormancy: dissolved oxygen, pH, and maternal investment impact Bythotrephes longimanus resting egg emergence and neonate condition

Abstract

Bythotrephes longimanus (Onychopoda: Cercopagidae), an invasive zooplankter in North America, requires suitable habitat to satisfy its planktonic and resting stages, which occupy the pelagia and sediment of lakes, respectively. Thousands of resting eggs from hundreds of planktonic mothers were exposed to laboratory conditions that mimicked gradients observed in lake sediment (dissolved oxygen = 1.4-11.9 mgÁL -1 ; pH = 3-11). Eggs hatched in all treatments, which confirms the utility of dormancy and the robustness of the resting egg in B. longimanus. However, hatching success and neonate condition were greatest when dormancy conditions were maintained at near-saturated dissolved oxygen and nearneutral pH; deviations from these conditions resulted in prolonged development, smaller neonates, and the failure of many eggs to hatch. In addition to the influence of environmental conditions, heavier mothers produced larger eggs that hatched more frequently and resulted in heavier neonates. These maternal effects are likely due to greater energy investment by healthier mothers. This study suggests that nature and nurture influence dormancy success, and the results underscore that both life-cycle stages of B. longimanus need to be considered to understand its range expansion.Résumé : Bythotrephes longimanus (Onychopoda: Cercopagidae), un organisme zooplanctonique envahissant en Amérique du Nord, requiert un habitat adéquat pour répondre aux besoins de ses stades planctoniques et son stade de repos qui vivent respectivement dans la zone pélagique et les sédiments des lacs. Nous avons exposé des milliers d'oeufs de repos provenant de centaines de mères planctoniques à des conditions de laboratoire qui miment les gradients observés dans les sédiments lacustres (oxygène dissous = 1,4-11,9 mgÁL -1 ; pH = 3-11). Les oeufs ont éclos dans toutes les conditions expér-imentales, ce qui confirme l'importance de la dormance et la robustesse des oeufs de repos chez B. longimanus. Cependant, le succès de l'éclosion et la condition des nouveau-nés sont meilleurs lorsque les conditions de dormance se maintiennent à un niveau d'oxygène dissous s'approchant de la saturation et à un pH près de la neutralité; les écarts à partir de ces conditions ont pour résultat, un développement prolongé, une taille réduite des nouveau-nés et un insuccès de l'éclosion chez de nombreux oeufs. En plus de l'influence des conditions du milieu, les mères plus lourdes produisent des oeufs plus grands qui ont un taux d'éclosion plus élevé et donnent des nouveau-nés plus lourds. Ces effets maternels sont vraisemblablement dus à un investissement énergétique plus important par des mères en meilleure santé. Notre étude laisse croire que la nature et les conditions d'élevage influencent le succès de la dormance; nos résultats soulignent qu'il est néc-essaire de considérer les deux étapes du cycle biologique de B. longimanus pour comprendre l'expansion de son aire de ré-partition.[Traduit par la Rédaction]

Propagule pressure, Allee effects and the probability of establishment of an invasive species (Bythotrephes longimanus)

“…Once counted, resting eggs were transferred into environmental growth chambers. Hatching experiments were conducted in the laboratory in order to facilitate monitoring, using established methodology for hatching Bythotrephes resting eggs (Brown 2008). Resting eggs were placed in jars covered by 100 lm mesh in groups of 10.…”

“…The aquaria were stored at 48C in the dark for four months to simulate overwintering conditions in lakes. After this period, the temperature in the chamber was raised to 6.58C to promote hatching (Brown 2008). Hatching was monitored weekly for four months and the percentage of eggs hatched from each enclosure that had produced resting eggs was calculated.…”

The effect of lake sediment on the hatching success of Daphnia ephippial eggs

“…Similar effects of anoxia were observed also in Artemia (Clegg, 1997). We are not aware of any reports showing the inhibitory effect of anoxia on the hatching of cladoceran dormant eggs, but we expect there to be one, as it was proven that incubation in water with higher oxygen concentrations results in higher hatching rates from Daphnia magna (De Meester, 1993) and Bythotrephes longimanus (Brown, 2008) dormant eggs than incubation in water of low oxygen content. Moreover, Carvalho and Wolf (1989) suggested that anoxic conditions can prolong diapause in Daphnia.…”

Population regulation of the spiny water flea (Bythotrephes longimanus) in a reservoir: Implications for invasion

“…Evidence from other studies suggests that reservoirs tend to have larger watershed-area : lake-volume ratios than natural lakes and this may be one factor contributing to their productivity (Havel et al 2005). Increased food availability may facilitate not only larger populations that are less vulnerable to Allee effects but may also permit more expansive in-lake dispersal of planktonic and resting stages (Brown 2008), which could improve survivorship and enhance establishment success. Associations between species establishment success and periods or locations of surplus resource availability have been demonstrated widely in terrestrial plants (Davis et al 2000).…”