Phosphorus content in detritus controls life history traits of a
detritivore
Michael Danger, Julio Arce Funck, Simon Devin, Julie Heberle and
Vincent Felten
Since most living plant material is not
consumed by herbivores, many
ecosystems rely on plant detritus (leaf
litter, dead wood…) as the main source of
nutrients and energy. Detritus is then
consumed by detritivores (mainly
invertebrates), these organisms
representing the essential basis of food
chains. Forested headwater streams are
typical detritus-based ecosystems where
the detritivore communities are often
dominated by insect larvae and small
crustaceans. In Western Europe,
Gammarus fossarum is one of the most
common crustacean detritivores found in
small forested streams, where it
represents an important component of
fish diet.
A central question in ecology concerns the
drivers of biological production and, in
particular, which factors limit organisms’
growth and development. For decades,
food quantity available for consumers has
been considered as the most important
parameter controlling organisms’ growth.
More recently, it has been proposed that
food content of some essential chemical
elements (food quality) could be directly
involved in the control of organisms’
growth. Among these chemical elements,
phosphorus is a key component of many
biological molecules (such as DNA or RNA)
and it is now recognized that this element
can potentially limit the growth and
reproduction of many herbivore species.
Despite the importance of detritus-based
ecosystems on Earth, extremely few data
are available on the role of detritus
chemical element content for detritivore
species.
Precopulatory mate guarding in Gammarus
fossarum (Crustacea Amphipoda; male above)
and details of the primary flagellum segments
counted to assess gammarids molts.
In this study, we manipulated the
phosphorus content of two leaf litter types
resulting in a large gradient of detritus
chemical quality. The detritus was then
used to feed individual G. fossarum during
a 5-week experiment under controlled
conditions. Size growth, mass growth and
molt number were determined throughout
the experiment. Our results showed for
the first time that phosphorus enrichment
of detritus led to faster growth of
detritivores, whatever the leaf litter type
considered. For both leaf litter types,
survival rate of G. fossarum was positively
correlated with detritus phosphorus
content. This study sheds new light on the
importance of phosphorus content of
detritus for detritivorous organisms, and
paves the way for further studies aimed at
understanding the physiology of
detritivores and the functioning of
detritus-based ecosystems.