Comparative Study of Brain Size Ontogeny: Marsupials and Placental Mammals

Abstract

There exists a negative allometry between vertebrate brain size and body size. It has been well studied among placental mammals but less is known regarding marsupials. Consequently, this study explores brain/body ontogenetic growth in marsupials and compares it with placental mammals. Pouch young samples of 43 koalas (Phascolarctos cinereus), 28 possums (Trichosurus vulpecula), and 36 tammar wallabies (Macropus eugenii) preserved in a solution of 10% buffered formalin, as well as fresh juveniles and adults of 43 koalas and 40 possums, were studied. Their brain size/body size allometry was compared to that among humans, rhesus monkeys, dogs, cats, rats, guinea pigs, rabbits, wild pigs, and mice. Two patterns of allometric curves were found: a logarithmic one (marsupials, rabbits, wild pigs, and guinea pigs) and a logistic one (the rest of mammals).

Keywords: brain variability; brain/body allometry; logarithmic/logistic curves; neuronal units; ontogenesis.

Figure 1

(a) Data from Figure 1b–h. (b) Data collected for this study. (c) Data from De Miguel and Henneberg, 1988 [28]. (d) Data from Janssens et al., 1997 and this study [24]. (e) Data from Nelson, 1988 [23]. (f) Data from Dobbing and Sands, 1970 [29]. (g) Data from Harel et al., 1972 [30]. (h) Data from Dickerson and Dobbing, 1967 [31].

Figure 1

(a) Data from Figure 1b–h. (b) Data collected for this study. (c) Data from De Miguel and Henneberg, 1988 [28]. (d) Data from Janssens et al., 1997 and this study [24]. (e) Data from Nelson, 1988 [23]. (f) Data from Dobbing and Sands, 1970 [29]. (g) Data from Harel et al., 1972 [30]. (h) Data from Dickerson and Dobbing, 1967 [31].

Figure 1

(a) Data from Figure 1b–h. (b) Data collected for this study. (c) Data from De Miguel and Henneberg, 1988 [28]. (d) Data from Janssens et al., 1997 and this study [24]. (e) Data from Nelson, 1988 [23]. (f) Data from Dobbing and Sands, 1970 [29]. (g) Data from Harel et al., 1972 [30]. (h) Data from Dickerson and Dobbing, 1967 [31].

Figure 2

(a) Data from Figure 2b–h. (b) Data from Passingham, 1975; Harel et al., 1972 [4,30]. (c) Data from Count, 1947; Dobbing and Sands, 1973; Connolly, 1950; Spector, 1956; Dickerson et al.; 1982; Zilles, 1972; Kretschmann et al., 1986 [1,32,33,34,35,36,37]. (d) Data from Holdt et al., 1975; Falk et al., 1999 [3,38]. (e) Data from Agrawal et al., 1968 [39]. (f) Data from Agrawal et al., 1967 [40]. (g) Data from De Souza and Dobbing, 1971 [41]. (h) Data from Agrawal et al., 1968 [42].

Figure 2

(a) Data from Figure 2b–h. (b) Data from Passingham, 1975; Harel et al., 1972 [4,30]. (c) Data from Count, 1947; Dobbing and Sands, 1973; Connolly, 1950; Spector, 1956; Dickerson et al.; 1982; Zilles, 1972; Kretschmann et al., 1986 [1,32,33,34,35,36,37]. (d) Data from Holdt et al., 1975; Falk et al., 1999 [3,38]. (e) Data from Agrawal et al., 1968 [39]. (f) Data from Agrawal et al., 1967 [40]. (g) Data from De Souza and Dobbing, 1971 [41]. (h) Data from Agrawal et al., 1968 [42].

Figure 2

(a) Data from Figure 2b–h. (b) Data from Passingham, 1975; Harel et al., 1972 [4,30]. (c) Data from Count, 1947; Dobbing and Sands, 1973; Connolly, 1950; Spector, 1956; Dickerson et al.; 1982; Zilles, 1972; Kretschmann et al., 1986 [1,32,33,34,35,36,37]. (d) Data from Holdt et al., 1975; Falk et al., 1999 [3,38]. (e) Data from Agrawal et al., 1968 [39]. (f) Data from Agrawal et al., 1967 [40]. (g) Data from De Souza and Dobbing, 1971 [41]. (h) Data from Agrawal et al., 1968 [42].

Figure 2

(a) Data from Figure 2b–h. (b) Data from Passingham, 1975; Harel et al., 1972 [4,30]. (c) Data from Count, 1947; Dobbing and Sands, 1973; Connolly, 1950; Spector, 1956; Dickerson et al.; 1982; Zilles, 1972; Kretschmann et al., 1986 [1,32,33,34,35,36,37]. (d) Data from Holdt et al., 1975; Falk et al., 1999 [3,38]. (e) Data from Agrawal et al., 1968 [39]. (f) Data from Agrawal et al., 1967 [40]. (g) Data from De Souza and Dobbing, 1971 [41]. (h) Data from Agrawal et al., 1968 [42].