INT. J. BIOL. BIOTECH., 10 (4): 515-536, 2013. PARENTAL INVESTMENT OF BIOMASS IN POD, SEED AND SEED PACKAGING IN A TREE OF WIRY WATTLE (ACACIA CORIACEA SUBSP. PENDENS) GROWING IN KARACHI, PAKISTAN D. Khan, Zulfiqar Ali Sahito and M. Javed Zaki Department of Botany, University of Karachi, Karach-75270, Pakistan. ABSTRACT One hundred and five mature pods from a solitary tree of Acacia coriacea subsp. pendens Gowen and Muskin growing in Botanical Garden of University of Karachi, Pakistan, were collected in the month of March 2012 and studied for various size parameters after air-drying for around two months. The pod weight averaged to 2.23 ± 0.073g (ranging from 0.9965 to 4.8622g) and tended to distribute normally. The number of mericarps per pod varied by 26.99% and averaged to 7.24 ± 0.19. The brood size averaged to 4.37 ± 0.19 seeds and tended to be positively skewed. The frequency of pods containing seed in each mericarp was low (10%). Ninety per cent of the pods had one or more empty seed chambers. The seed mass per pod varied by a quantum of 44.35% and averaged to 0.5834 ± 0.2892 g and maximally 1.2572g in one pod. The pericarp mass of pods varied from 0.4934 to 3.5002g per pod (CV: 31.6%). The weight of single seed for a sample of 399 normal seeds collected from 105 pods was less variable (15.58%) as compared to the brood size (CV: 44.35%). The weight of individual seed averaged to 139.70 ± 1.0827 mg varying from 58.4 to 243.7 mg (4.17 -fold variation). The distribution of seed weight of normal seeds was asymmetrical (negatively skewed). The proportion of pericarp to fruit (PFR) was 73.26 ± 0.899% and proportion of seeds to fruit (SFR) was 24.45± 0.816%. There was a positive linear relationship between logarithms of seed yield per pod and mass of the pod (r = 0.7878). The slope of the line (b) was 1.3766, not significantly different from 1 (t = 0.266, NS). Also, there was significant positive linear relationship between log (number of seeds per pod) and log (pod mass). The slope (b = 1.0594) of the regression was not significantly different from 1 (t = 0.495, NS). The investment in pericarp declined with increase of brood size significantly. The increase in brood size in a pod associated positively with seed mass proportion to pod mass but negatively with pericarp proportion to pod mass. The seed packaging costs for 105 pods was expressed on the basis of pericarp [g.g -1 seeds (SPC 1 )] and pericarp [g per seed (SPC 2 )]. The SPC 1 averaged to 3.6399 ± 0.2197 g.g -1 seeds and SPC 2 averaged to 0.4277 ± 0.0231 g per seed varying by 69.03 and 55.8%, respectively. On individual seed basis, seed packaging cost was 3.06 times of the average seed weight. SPC 1 and SPC 2 both distributed asymmetrically (positively skewed) i.e. the magnitude of the SPC was quite high in few pods - generally those yielding single seed. On an average 72.35% of the pod mass was allocated to protection and nutrition of seeds, 25.3% to seed production and 2.39% to the aril (elaiosome) for dispersal due to birds or ants. Key Words: Acacia coriacea subsp. pendens, insect pest, parental investment of biomass, pod- and seed- and elaiosome-size variation, seed Packaging cost. INTRODUCTION The quantification of reproductive allocation at fruit and seed levels has been made in several ecological studies (Willson et al., 1990; Lee et al., 1991; Lord and Westoby, 2006; Martinez et al., 2007; Chen et al., 2011, Khan and Zaki, 2012; Khan and Sahito, 2013). Angiospermic seeds developing from ovules are enveloped in Pericarp. Seeds give rise to seedlings and pericarp provide protection and nutrition to seeds and at times dispersal. Pericarp occupies significantly varying proportion of the fruit biomass. Determining within fruit reproductive allocation is important for the understanding of reproductive bionomics and seed size significance in plant life strategy (Chen et al., 2010). Some ecologists have been interested in examining the scaling relationship between the seed packaging, and the individual seed mass. Such studies are likely to be important and interesting (Mehlman, 1993) since pattern of seed- packaging varies significantly among broadly ecologically similar species and within species (Willson et al., 1990; Chen et al., 2010; Khan and Zaki, 2012, Khan and Sahito, 2013). In this paper, variation in pod-, seed sizes and seed packaging costs and seed weight-seed number relationship within an individual tree of Acacia coriacea subsp. pendens Cowen and Maslin, an Australian wiry wattle growing in Botanical Garden, University of Karachi, Pakistan, is studied. This plant is native of Western Australia. A. coriacea grows well in sand dunes (coastal), ridges, and rocky limestone hills, in deep sands/ soils. A. coriacea is reported to have several uses – fuel wood. Fodder and planting (Thomson and Cole, 1987). Its flowers are edible – used in flitters. Seeds are sweet and nutritious (www. P.faf.org/user/plant.aspx?Latinname=Acacia+ Coriacea). Description of the area (Climate) Aridity is the basic characteristic of physical environment of Karachi, where from the isocline of -50 moisture