| dc.description.abstract | Parental protection in aquatic systems is usually related to the aggregation of the
offspring. Many studies suggest that oxygen and food availability to the aggregation are
important limiting factors affecting survival and development of embryos. Spite of this
general consensus, there are few studies addressing how those factors are interacting
and operating on species with different developmental modes and the potential larval
and maternal responses to reduce the effect of both limitations. Moreover, there are no
studies evaluating the potential role of oxygen and food limitations to determine
parental protection time and in last term, the developmental mode of marine
invertebrates. Additionally, alternative approaches such as the kin selection theory, have
not been explored in order to assess the importance of genetic factors to explain the
adaptative value of sorne developmental strategies that may pay a high cost in term of
fitness. Thus, in this thesis 1 atternpted to develop a more integrative view working on
two calyptraeid species with contrasting developmental modes and which encapsulate
and brood their offspring: Crepidula Jhrnicaia, an indirect developer with a free
planktotrophic larva and C. coquimbensis a species with direct development and
intracapsular sibling cannibalisrn. As all member of the Calypatreid group, both species
are protandrics. The general objective of this thesis was to evaluate maternal and
embryonic responses at genetic, physiological and behavioral levels that underlie the
solution of intracapsular food and oxygen availability between species with contrasting
developmental strategies and different embryo feeding behaviors. The niethodological
approach included: (1) evaluations of the potential use of dissolved albumen by larvae as an alternative intracapsular food source, (2) quantification of oxygen changes in the
intracapsular space and the incubation chamber throughout developmental time, (3)
quantification of changes in the embryonic metabolic rate, the metabolizing material
and capsule wall thickness with time, and (4) orthogonal experiments manipulating the
amount of food (dissolved protein) and oxygen available for the embryos. The main
variables of response were embryo survival and hatching size, both important life
history traits. Also, the sibling cannibalism of C. coquimhensis was studied under the
kin selection theory through experiments and paternity analyses. For that, cannibalism
rate was compared between artificial embryo aggregations with different levels of
relatedness after 40 days of cultivation. 1 evaluated ifsibling cannibalism is a random or
selective behavior comparing the total percentage of male participation per artificial
aggregation at the beginning and the end of the experiment. Also the relationship
between mate size and male reproductive success was studied under the resource
allocation theory. Paternity analyses on embryos were performed using five
hypervariable microsatellite markers. Finaily, the direct benefit of cannibalism on
juvenile hatching size was quantified.
Comparative analyses of oxygen conditions in the intracapsular environment of
the two species showed clear differences between the species exhibiting direct
developrnent, C. coquimbensis, and indirect development, C. fornicala. While oxygen
conditions remained high in the first case, constant deterioration of intracapsular oxygen
conditions reaching almost anoxic levels toward late stages was observed in C.
fornicata. The differences observed can be explained by: (1) initial differences in
thickness wall between species, which may affect oxygen diffusion, and in the rate of
decay of the capsule wall throughout development, (2) differences in oxygen
consumption between species and in the rate of increase in oxygen demand toward late stages, and (3) differences in the anlount of metabolizing material between species and
throughout development. An artificial extension of the parental protection time showed
significant effects on larval survival of C. fornicata but not in C. coquimbensis. These
findings suggest the hypothesis that the persistence of an intermediate free living stage
in C Jornicata may be a response to oxygen constraints during time of protection,
constraining parental care. | |
