26.3 Wednesday, Jan. 4 Darwin in a nutshell – the subtle intracapsular survival of the fittest in the common whelk Buccinum undatum SMITH, K E*; THATJE, S; University of Southampton; University of Southampton Kathryn.Smith@noc.soton.ac.uk
Life history theories suggest parental fitness is maximised by investing equally into all offspring. The common whelk Buccinum undatum shows large differences in offspring investment. This species has intracapsular development, with nurse eggs consumed by developing embryos (adelphophagy). In most species exhibiting adelphophagy, nurse egg consumption occurs over weeks to months and nutritional distribution is about equal within a capsule. In B. undatum, nurse egg consumption occurs rapidly over a few days in which veligers compete for nurse eggs. Eggs are stored in the middle gut, ‘secured’ for later use. Asynchronous development leads to large differences in numbers of nurse eggs consumed by each veliger. One third of capsules examined held at least 1 veliger containing no nurse eggs. Number of developing veligers, nurse egg consumption and energetic fitness of veligers varied with capsule size and developmental temperature (6 to 18°C). During development ‘accidental cannibalism’ was observed. Older embryo’s consumed undeveloped embryo’s, morphologically identical to nurse eggs. Consumed embryos then developed and took up nurse eggs from inside the older embryo, which eventually died. Intracapsular resource partitioning observed in B. undatum is highly unusual, especially given the maternal energy investment put into each developing embryo. The high level of competition seen in each capsule leads to very uneven resource partitioning amongst offspring affecting size and energetic predisposition for later life. Ultimately this selection for the fittest inhibits the number of embryo’s successfully developing as some outcompete others for the limited resources.