Life history attributes such as rates of birth, death, growth, and development typically are related in predictable ways that support distinct, but successful, life styles. Typically, birth rate and adult longevity are negatively correlated and development time and life-time survival are positively correlated. Slow development and low fecundity are thought to be essential to a life history that includes long maximum life spans and are thought to have their effects through improving the health and survival of offspring. However, tropical birds of Asia appear to violate this pattern, being similarly long-lived to the birds of the New World tropics, but having higher fecundity and development rate. Therefore, low fecundity and slow development may not be necessary for high offspring quality and long life. This study will use extensive and detailed comparative surveys, complemented with some field experimentation, to examine possible environmental causes of the higher fecundity and faster development of 25-30 bird species in Sabah, Malaysia. Additionally, the work will examine the extent to which fecundity and development rate determine offspring immune function and thereby determine adult longevity.
This work will provide new insight into the roles of development rate and fecundity in the ability to fight pathogens through immune function and of the influence of this and other indicators of offspring quality on longevity. It also will improve understanding of the environmental causes of variation in rates of birth, death, and development and their interrelationships. These rates greatly influence the vulnerability of populations to environmental change and can significantly aide our ability to sustain biodiversity in North America, as well as world-wide. Finally, this work includes substantial scientific training of many undergraduate and graduate students, including members of groups currently underrepresented in science.
Intellectual merit Tropical species generally produce fewer offspring that develop more slowly than north temperate relatives. Data from the literature for tropical Asia suggest that songbird clutch sizes are larger and more variable, and development is faster than for Neotropical songbirds. Both higher fecundity and faster development are expected to yield shorter life and higher adult mortality from physiological trade-offs. We explored these issues in tropical Asia in Kinabalu National Park, Malaysia at 6 degrees N latitude at elevations (1400 – 1950 m) that were comparable to studies we accomplished in the Neotropics in the Andes of Venezuela. We found that, contrary to the literature, neither clutch size nor development rates differed from the Neotropical site. Both tropical sites, however, differed from North Temperate sites, with fewer offspring and slower development in the tropics in both Asia and Neotropics. Length (i.e., speed) of embryonic development was only weakly explained by differences in embryo metabolism, contrary to long-standing expectations. Instead, variation in parental effort in warming embryos explained the vast majority of variation in embryonic development. Longer and slower development due to cold temperature does not provide the benefits for offspring quality and adult survival expected under physiological trade-offs. Once temperature is accounted for, then remaining variation in development periods explains quality of offspring as measured by their immune function. I proposed a new hypothesis and provided evidence that mothers may advance provision offspring against reduced attentiveness during incubation by laying larger eggs. Egg size variation has long been attributed to a trade-off with number of eggs (clutch size), but this trade-off has repeatedly not been observed within birds. Cooler incubation temperatures from reduced parental effort creates energy costs for embryos, and I show for the first time that species with reduced parental effort and colder incubation temperatures lay larger eggs, independent of clutch size. These maternal effects may help compensate for the costs of lower parental effort during incubation. Growth rates of post-natal offspring are less sensitive to temperature because they develop the ability to produce their own heat (endothermy). Broad evidence in the literature and our studies show that variation in nest predation risk exerts selection on growth rates, with faster growth in species with higher risk. We show for the first time that faster growth was facilitated by selection from nest predation on nestling metabolism; species with higher nest predation risk had higher metabolism that was closely correlated with faster development. We also showed for the first time that growth rates are also facilitated by differential development of body parts, with priority given to locomotor modules and development of endothermy, all of which allow earlier escape of risky nests. This variation has gone unrecognized, but I proposed that this variation may be critical in underlying evolution of offspring number. Broader impacts The project provided support for three graduate students to continue their experiments and observations that serve as major components of their dissertation research. I spend the first 6 weeks in the field with the students discussing experimental design and results. I also spend significant time meeting with them outside the field season to discuss scientific theory and approaches to enhance their development as scientists. Besides the 3 graduate students, the project also supported > 60 individuals in the field and lab, with most being undergraduate students, but also including post-undergraduate individuals preparing to apply for graduate school, and Malaysians. These individuals included about 50% females, numerous minorities, and several Malaysians. These were trained in a wide variety of field techniques, and taken through the theory of the science underlying the research being conducted, as well as strong inference science reasoning based on powerpoint presentations. One individual has developed a manuscript on the breeding biology of one of the species for which nothing is known previously. I have worked with him on statistical analyses and writing. It is in its second draft. I helped another with a manuscript she was developing based on work from a different project. A powerpoint presentation was made to National Park personnel, and members of the tourism board in Sabah, Malaysia. We also developed short YouTube videos of bird breeding behavior from the site to engage the general public: www.youtube.com/user/BirdNestingBehavior We continue to develop these videos. Finally, results are being made available through peer-reviewed publications.
