Marine invertebrates display a range of complex life-history strategies. In general, larvae fall into one of two groups. They either meet the nutritional requirements of development by feeding during the larval phase or, they depend on nutrients supplied by the mother. Very rarely they can do both. These so-called ‘facultative feeders’ get a benefit from feeding but can, if necessary, complete larval development without food.
Alex Gangur and supervisor Dustin Marshall have found that a small crustacean can be added to this relatively short list of species that incorporate facultative feeding into the larval stage. Alex uses the copepod Tisbe sp. as his model species in a series of long-term experiments but he was surprised when he noticed that some of the larvae seemed to survive without food.
Alex and Dustin designed a series of experiments to determine if Tisbe was indeed a facultative feeder and, if so, what was the cost of completing development without food? They were also interested in how temperature might affect the outcomes as temperature is well known to have a strong relationship with larval development.
They set up a series of experiments where newly hatched larvae were assigned to vials with or without food and to one of two temperatures and individuals were monitored through metamorphosis and until they reproduced or died.
They found that a proportion of the starved copepods not only survived but went on to reproduce. But there was a cost. Development time was much longer in starved copepods compared to those that were fed and a higher temperature reduced development time in both feeding and starved copepods. The size of juveniles immediately after metamorphosis was smaller in starved copepods.
Surprisingly, there was little carryover of the larval experience in the time to maturity or reproductive effort. Instead, the amount of food received as a juvenile was more important. But, more work is needed on the impacts of larval starvation on adult performance and, in particular, the effects of larval starvation on lifetime reproductive rate.
It is always difficult to extrapolate from lab experiments to real-world situations but the ability to complete larval development and metamorphosis in the absence of food likely provides an important buffer to populations experiencing fluctuating food availability.