Phocoena Phocoena
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Recent papers in Phocoena Phocoena
In morphological traits, variation within species is generally considered to be lower than variation among species, although this assumption is rarely tested. This is particularly important in fields like palaeontology, where it is common... more
In morphological traits, variation within species is generally considered to be lower than variation among species, although this assumption is rarely tested. This is particularly important in fields like palaeontology, where it is common to use a single individual as representative of a species due to the rarity of fossils. Here, we investigated intraspecific variation in the cochleae of harbour porpoises (Phocoena phocoena). Interspecific variation of cochlear morphology is well characterised among odontocetes (toothed whales) because of the importance of the structure in echolocation, but generally these studies use only a single cochlea to represent each species. In this study we compare variation within the cochleae of 18 specimens of P. phocoena with variations in cochlear morphology across 51 other odontocete species. Using both 3D landmark and linear measurement data, we performed Generalised Procrustes and principal component analyses to quantify shape variation. We then quantified intraspecific variation in our sample of P. phocoena by estimating disparity and the coefficient of variation for our 3D and linear data respectively. Finally, to determine whether intraspecific variation may confound the results of studies of interspecific variation, we used multivariate and univariate analyses of variance to test whether variation within the specimens of P. phocoena was significantly lower than that across odontocetes. We found low levels of intraspecific variation in the cochleae of P. phocoena, and that cochlear shape within P. phocoena was significantly less variable than across odontocetes. Although future studies should attempt to use multiple cochleae for every species, our results suggest that using just one cochlea for each species should not strongly influence the conclusions of comparative studies if our results are consistent across Cetacea.
A total of 1,268 harbour porpoises were obtained from fishing nets in Icelandic coastal waters from September to June in the years 1991 to 1997. Foetal sex ratio was 1.2:1 (male:female). The bias towards males increased further among... more
A total of 1,268 harbour porpoises were obtained from fishing nets in Icelandic coastal waters
from September to June in the years 1991 to 1997. Foetal sex ratio was 1.2:1 (male:female). The
bias towards males increased further among older animals in the present collection. The modal
year classes were 0 and 1 years but the oldest porpoise was a female estimated at 20 years of age.
Length at birth was estimated as approximately 75 cm, and females grew faster and attained larger sizes than males. Asymptotic length was 149.6 cm for males and 160.1 cm for females. Estimated
age and length at sexual maturity was 1.9 to 2.9 years and 135 cm for males and 2.1 to 4.4 years
and 138 to 147 cm for females. Immature individuals were significantly shorter than pubertal and
mature animals in both sexes in age classes 1 to 3. Testes weight increased only slightly with body
size in immature males but increased rapidly around maturity. Pronounced seasonality was also
observed in testes weight, indicating a peak in testes activity in summer. Lack of data from the
summer makes the exact timing of parturition and mating unknown. Births do, however, most
likely peak in June and July and lactation lasts at least 7 to 8 months. Ovulation and pregnancy
rates were 0.98.
from September to June in the years 1991 to 1997. Foetal sex ratio was 1.2:1 (male:female). The
bias towards males increased further among older animals in the present collection. The modal
year classes were 0 and 1 years but the oldest porpoise was a female estimated at 20 years of age.
Length at birth was estimated as approximately 75 cm, and females grew faster and attained larger sizes than males. Asymptotic length was 149.6 cm for males and 160.1 cm for females. Estimated
age and length at sexual maturity was 1.9 to 2.9 years and 135 cm for males and 2.1 to 4.4 years
and 138 to 147 cm for females. Immature individuals were significantly shorter than pubertal and
mature animals in both sexes in age classes 1 to 3. Testes weight increased only slightly with body
size in immature males but increased rapidly around maturity. Pronounced seasonality was also
observed in testes weight, indicating a peak in testes activity in summer. Lack of data from the
summer makes the exact timing of parturition and mating unknown. Births do, however, most
likely peak in June and July and lactation lasts at least 7 to 8 months. Ovulation and pregnancy
rates were 0.98.