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Mortality of Pentactulae During Intraovarian Brooding in the Apodid Sea Cucumber Leptosynapta clarki
Insights
A new method using calcareous rings of Leptosynapta clarki embryos estimates brooding mortality. This method reveals variable mortality, including total brood loss in some marine invertebrates.
Area of Science:
- Marine Biology
- Developmental Biology
- Invertebrate Zoology
Background:
- Estimating embryonic mortality in brooding marine invertebrates is challenging due to the lack of reliable methods to determine initial embryo numbers.
- Existing methods are limited, hindering accurate assessments of developmental mortality rates.
Purpose of the Study:
- To develop and validate a reliable method for estimating initial embryo numbers in brooding Leptosynapta clarki.
- To quantify mortality rates during brooding in L. clarki and explore potential implications for nutrition and life history evolution.
Main Methods:
- Utilizing the calcareous ring of pentactulae (larval stage) of Leptosynapta clarki as a persistent indicator of initial embryo presence.
- Analyzing the retention of calcareous rings within the ovary throughout the brooding period.
- Estimating instantaneous mortality rates based on the presence and persistence of calcareous rings.
Main Results:
- The calcareous ring is present for approximately 93% of the brooding period and is retained in the ovary, making it a reliable marker.
- Mortality rates in Leptosynapta clarki were variable, with some females experiencing up to 100% brood loss.
- Estimated instantaneous mortality rates ranged from 0 to -0.0114 d-1, comparable to other brooding marine invertebrates.
Conclusions:
- The calcareous ring method provides a robust tool for estimating initial embryo numbers and subsequent mortality in brooding invertebrates.
- Variable embryonic mortality, including total brood loss, is a significant factor in L. clarki and potentially other marine invertebrates.
- The resorption of dead embryos may contribute to the nutrition of surviving embryos, and the retention of hard embryonic structures offers insights into invertebrate life history evolution.
Abstract:
Estimates of mortality during development in brooders have been restricted by the lack of a reliable method for determining the number of embryos at the start of brooding. The calcareous ring of the pentactulae of Leptosynapta clarki can be used to determine initial embryo number because the ring is present for about 93% of the brooding period, is retained within the ovary, and is not resorbed after embryo death. Pentactulae mortality was found to be variable in female Leptosynapta clarki, with up to 100% mortality (= total brood loss) in some females. Estimates of instantaneous mortality in L. clarki ranged from 0 to -0.0114 d-1 and were of similar magnitude to those for other brooding marine invertebrates. The resorption of dead pentactulae in the ovary may provide additional material to the ovarian fluid for the nutrition of living pentactulae. The retention of hard embryonic structures (e.g., calcareous parts, shells) in other brooding marine invertebrates may allow further estimates of mortality during brooding, and provide an insight into the importance of embryo mortality in the evolution of marine invertebrate life histories.
