Facultative Matrotrophy in the Livebearing Fish, Gambusia geiseri: Implications for the Evolution of Matrotrophy in the Family Poeciliidae

活鱼科鱼类的发育策略多种多样。在孔雀鱼中，幼鱼通过储存在巨大的卵黄中的能量在卵巢中发育(卵磷脂营养)，而在最小的鲤鱼中，卵非常小，几乎没有卵黄，大多数发育和生长的能量通过胎盘状结构(专性母体营养)从母亲转移到胚胎。其他物种表现出一种混合的策略，在这种策略中，储存在相对较大的卵子中的能量由胚胎发育期间母体营养的转移来补充(补充配种)。一种特定物种表现出的策略类型被认为是反映其所处环境的生产力。专性滋养物预计只有在母亲的食物充足和可预测的高生产力环境中才会出现。在生产率较低或不可预测的环境中，卵磷脂营养是预期的策略。表现补充母性生殖的物种可能生活在不可预测的环境中，但如果出现多余的食物，它们能够利用多余的食物，并将额外的能量传递给发育中的后代(兼性补充母性生殖)。传统上，大额配子被认为是严格的卵磷酸盐营养，但最近的研究表明，尽管没有明显的胎盘结构，但这种物种的营养物质可以从母体转移到胚胎。这项研究建议使用放射性标记的营养物质来量化大型河豚的营养贡献，以解决以下问题：母体-胚胎移植表面的性质以及它如何限制转移的营养物质的数量或类型？在自然条件下，大型银杏在多大程度上表现出母性营养？在给定种群内和不同种群之间，母性营养的贡献如何随环境条件的变化而变化？理解兼性生殖营养的发生，无论是在顶端还是在栖息地内，可能有助于解释斑点鱼科内不同的发展策略以及这些策略与环境生产力的关系。此外，兼性生殖策略本身可能反映了对不可预测环境的适应，允许表现出这一策略的物种占据经历自然环境变化的栖息地。因此，这一策略可能会为人类引起的环境变化提供重要的缓冲。

Livebearing fishes of the Family Poeciliidae exhibit a variety of developmental strategies. In theguppy, young develop in the ovary from the energy stored in large, yolky eggs (lecithotrophy), whereas inthe least killifish, the eggs are very small, with little yolk, and most energy for development and growth istransferred from the mother to the embryo through a placenta-like structure (obligate matrotrophy). Otherspecies exhibit a mixed strategy in which energy stored in relatively large eggs is supplemented bymaternal transfer of nutrients during embryonic development (supplemental matrotrophy). The type ofstrategy exhibited by a given species has been suggested to reflect the productivity of the environmentthat it inhabits. Obligate matrotrophs are predicted to occur only in highly productive environments wherefood for the mother is abundant and predictable. In less productive or less predictable environments,lecithotrophy is the expected strategy. Species that exhibit supplemental matrotrophy may inhabitunpredictable environments but be capable of exploiting excess food if it occurs and passing extra energyon to developing offspring (facultative supplemental matrotrophy).The largespring gambusia has traditionally been considered to be strictly lecithotrophic, butrecent studies have demonstrated mother-to-embryo transfer of nutrients in this species despite theabsence of an obvious placental structure. This study proposes to use radiolabeled nutrients to quantifymatrotrophic contribution in largespring gambusia in order to address the following questions: What isthe nature of the mother-embryo transfer surface and how does it limit the amount or types of nutrientstransferred? To what extent does the largespring gambusia exhibit matrotrophy under natural conditions?How does matrotrophic contribution vary with environmental conditions within a given population andamong different populations? Understanding the occurrence of facultative matrotrophy, both acrosshabitats and temporally within habitats, may help explain the variety of developmental strategies withinthe Family Poeciliidae and the relationship of those strategies to environmental productivity. Furthermore,the strategy of facultative matrotrophy itself may reflect an adaptation to unpredictable environments thatallows species exhibiting this strategy to occupy habitats that undergo natural environmental variation.This strategy, then, may provide an important buffer against human-induced environmental changes.