Context Of Life History Theory Research Articles

Growth, Development, and Life History throughout the Evolution ofHomo

For over a century, paleoanthropologists have listed the presence of prolonged periods of gestation, growth, and maturation, extremely short interbirth intervals, and early weaning among the key features that distinguish modern humans from our extant ape cousins. Exactly when and how this particular scheduling of important developmental milestones—termed a “life history profile”—came to characterize Homo sapiens is not entirely clear. Researchers have suggested that the modern human life history profile appeared either at the base of the hominin radiation (ca. 6 Ma), with the origins of the genus Homo (ca. 2.5 Ma), or much later in time, perhaps only with H. sapiens (ca. 200–100 Ka). In this short review, evidence of the pace of growth and maturation in fossil australopiths and early members of Homo is detailed to evaluate the merits of each of these scenarios. New data on the relationship between dental development and life history in extant apes are synthesized within the context of life history theory and developmental variation across modern human groups. Future directions, including new analytical tools for extracting more refined life history parameters as well as integrative biomechanical and developmental models of facial growth are also discussed.

Growth and reproduction of introduced goldfish Carassius auratus in small ponds of southeast England with and without native crucian carp Carassius carassius

The ornamental Asiatic species, goldfish Carassius auratus, was introduced to open waters of the UK in the late 17th century. The species reproduces readily in small ponds and threatens native species, in particular crucian carp Carassius carassius, but surprisingly there are no known published studies on the growth and reproduction of feral pond populations of this species in the UK and relatively few elsewhere. The aim of the present study was to assess the growth (back-calculated length at age), body condition and reproduction (fecundity, egg size, length and age at maturity) of goldfish living in small ponds of Epping Forest (northeast London, England), either alone (allopatry) or with (sympatry) native crucian carp, in order to provide the necessary background information to inform the risk assessment of this non-native fish species. Growth increments in the allopatric goldfish populations were similar, with progressively declining growth increments with increasing age. This contrasts with goldfish living in sympatry with crucian carp Carassius carassius, where growth increments remained high for ages 1–2, 2–3 and 3–4. Body condition values varied little, but goldfish living in allopatry had significantly greater condition than those living in sympatry with crucian carp. Sexual maturity was achieved by at least some age 1+ fish in all populations, with young mean ages (1.0–1.7 years) and short mean standard lengths (50.0–63.4 mm SL) at maturity in females relative to an introduced population in Italy (2.1 years and 139.2 mm SL, respectively). The results are discussed within the context of life-history theory.

Constitutive immune defences correlate with life‐history variables in tropical birds

1. It has been suggested that immune defences are shaped by life history and ecology, but few general patterns have been described across species. We hypothesized that 'fast' life-history traits (e.g. short development times, large clutch sizes) would be associated with developmentally inexpensive immune defences, minimizing the resource demands of young animals' immune systems during periods of rapid growth. Conversely, 'slow' life histories should be associated with well developed antibody-mediated defences, which are developmentally costly. 2. We therefore predicted that 'fast-living' species would exhibit higher levels of complement proteins, a component of non-specific innate defence, but lower levels of constitutive ('natural') antibodies. Additionally, we predicted that constitutive immune defences in general would be higher in species with ecological characteristics that might increase exposure to pathogens, such as open nests, omnivorous diets, gregariousness, and closed forested habitat. 3. Across 70 Neotropical bird species, we found a strongly positive relationship between incubation period and natural antibody levels in adult birds, suggesting that longer developmental times might allow the production of a more diverse and/or more reactive adaptive immune system. Complement activity was positively, although weakly, correlated with clutch size, providing some support for the hypothesis that faster-living species rely more on innate defences, such as complement. Unexpectedly, solitary species had higher natural antibody titres than species that frequently join flocks. 4. Our results suggest that, despite probably widespread differences in the intensity and diversity of pathogen exposure, species-level variation in constitutive immune defences is understandable within the context of life-history theory.

Reproductive Responses of Five White Sucker (Catostomus commersoni) Populations in Relation to Lake Acidity

White sucker (Catostomus commersoni) in three acid lakes (pH 4.90, 5.56, and 5.58) frequently matured at older ages and larger sizes and had shorter reproductive life spans than white sucker in two circumneutral lakes (pH 6.30 and 6.35). Reproductive life span was positively correlated in females (r = 0.97) and males (r = 0.85) with lake pH. In the acid lakes, elevated mortality rates coincided with the onset of sexual maturity whereas in circumneutral lakes, mortality rates did not change at maturity. Ovarian weight and ovarian somatic index values were not significantly different between females from two acid and two circumneutral lakes. Values of fecundity, ova dry weight, testicular weight, and testicular somatic index of fish in acid lakes were either significantly greater than or equal to values in white sucker from circumneutral lakes. Results are discussed within the context of life history theory.