Phylogenetic Patterns of Size and Shape of the Nasal Gland Depression in Phalacrocoracidae

--Nasal glands in Pelecaniformes are situated within the orbit in closely fitting depressions. Generally, the depressions are bilobed and small, but in Phalacrocoracidae they are more diverse in shape and size. Cormorants (Phalacrocoracinae) have small depressions typical of the order; shags (Leucocarboninae) have large, single-lobed depressions that extend almost the entire length of the frontal. In all Phalacrocoracidae I examined, shape of the nasal gland depression did not vary between freshwater and marine populations. A general linear model detected strongly significant effects of species identity and gender on size of the gland depression. The effect of habitat on size was complex and was detected only as a higher-order effect. Age had no effect on size or shape of the nasal gland depression. I believe that habitat and diet are proximate effects. The ultimate factor that determines size and shape of the nasal gland within Phalacrocoracidae isphylogenetic history. Received 28 February 1989, accepted 1 August 1989. THE FIRST investigations of the nasal glands of water birds indicated that these glands were more developed in species living in marine habitats than in species living in freshwater habitats (Heinroth and Heinroth 1927, Marpies 1932). Schildmacher (1932), Technau (1936), and others showed that the degree of development among species was associated with habitat. Later experimental studies (reviewed by Holmes and Phillips 1985) established the role of the nasal gland as an extrarenal excretory organ that maintains electrolyte homeostasis and water balance during conditions of salt-loading. The size of the nasal gland and its degree of function varies also within species. Marine populations have larger glands and greater functional activity than do freshwater populations of a given species (Schmidt-Nielsen 1959, 1960, 1965; Peaker and Linzell 1975). Experimental studies with captive wild and domestic birds indicate that gland size (i.e. mass) and function increased quickly in individuals of some species when subjected to high electrolyte stress or low water intake (Holmes et al. 1961, Ellis et al. 1963, Peaker and Linzell 1975). In other species, accommodation to salt-loading is less effective (Skadhauge 1981). Development and growth rate in captive Mallards (Anas platyrhynchos) that were fed 1% solutions of sodium chloride were reduced compared with development and growth of birds fed fresh water (Schmidt-Nielsen and Kim 1964). Data from field populations of wild birds are uncommon (e.g. Technau 1936, Zaks and Sokolova 1961, Thomson and Morley 1966), and only a few studies have focused on the cranial structure associated with the nasal gland (Marpies 1932; Bock 1958, 1963; Staaland 1967; Watson and Divoky 1971; Lavery 1972). Unlike most other birds, Pelecaniformes have nasal glands situated in depressions found in the anteromedial roof of the orbit (Siegel-Causey 1988). In species with extraor supraorbital nasal glands, glandular tissue can enlarge by growth outward from the skull (Owen and Kear 1972) and by increase in width (Bock 1958), but rarely by increase in length (Staaland 1967, Peaker and Linzell 1975). Because cranial bone is membranous, mesenchymal, and nonintussusceptive, and because it grows very slowly if at all after ossification and maturation (de Beer 1937, Bellairs and Jenkin 1960), change in bony outline of the gland depression must occur slowly. Thus, functionally induced growth of the nasal gland in the orbit is constrained in Pelecaniformes because substantial thickening of the gland without osteological accommodation could distort the eye. I have shown qualitatively (Siegel-Causey 1988) that the size and shape of the nasal gland depression is variable within shags and cormorants (Phalacrocoracidae). In this study, I surveyed the variation in size and shape of the nasal gland depression in the orbit of selected members of this family. I examined its presumptive association with gland size relative to 110 The Auk 107: 110-118. January 1990 January 1990] Phalacrocoracidae N sal Glands 111 Fig. 1. Outlines of the ventral view of the frontal bone and nasal gland depression in selected Pelecaniformes. All views represent the area indicated in Figure 2: lower; shaded areas represent the nasal gland depression: (a) Great Frigatebird; (b) White Pelican; (c) Red-footed Booby; (d) Northern Gannet; (e) Anhinga; (f) Little Pied Cormorant; (g) Olivaceous Cormorant (left, freshwater; right, marine); (h) Double-crested Cormorant (left, freshwater; right, marine); (i) Pied Cormorant; (j) Little Black Cormorant; (k) Brandt's Cormorant; (1) Black-faced Cormorant; (m) Socotra Shag; (n) Cape Shag; (o) Imperial Shag, marine (left, e; right, •); (p) Imperial Shag, freshwater (left, e; right, •); (q) Rock Shag; (r) Pelagic Shag; (s) Red-legged Shag. collection habitat, age (measured by size of bursa of Fabricius), size, and species identity.