Phytogeographical Distribution and Fruit Diversity of Lagenaria siceraria Species in Nigeria

Phytogeographical distribution and fruit diversity of Lagenaria siceraria (Mol.) Standl species in Nigeria were accessed. Information on the distribution and fruit diversity was sourced from three herbaria, Forestry Research Institute of Nigeria Herberia, University of Port Harcourt Herberia and the University of Ibadan Herberia. A field survey across fifteen states in Nigeria namely Kaduna, Kano, Plateau, Oyo, Akwa Ibom, Cross River, Taraba, Bayelsa and Enugu, Ebonyi, Ondo, Ogun, Kwara Anambra and Rivers State. A total of twen-ty-four fruit shapes were accessed. The diversity of fruit shapes across the geographical regions of Nigeria shows that the Guinea savannah has all the twenty-four different landraces represented, while Tropical rain forest has nineteen, Sudan savannah has seventeen and Freshwater swamp and the Saltwater swamp has eleven different fruit shapes respectively. The fruits of Lagenaria siceraria (Mol) Standl is considered a topocline since it is not affected only by environmental factors but possess a wide distribution pattern across the geographical regions of Nigeria.

Lagenaria siceraria (Mol.) Standl. has probably been domesticated independently in Africa, Asia and America and these demonstrations are reflected in the variability of commercial cultivars [7]. However, Decker-Walters D, et al. [9] discovered an additional wild indigenous species in Zimbabwe which reinforced the latter hypothesis of Africa as the centre of origin of Lagenaria siceraria species.
Varieties of Lagenaria siceraria (Mol.) Standl is known throughout West Africa, where it has been grown for containers, but these variants are largely unrecorded in terms of name and characteristics [5]. Brown University [10] has described phytogeography as the study of distribution of species and ecosystems in geographic space, through geological time. Organisms often vary along geographic gradients of latitude, elevation, isolation and habitat area. Modern phytogeography often employs the use of Geographic Information Systems GIS, to understand the factors affecting organism distribution, and to forecast future trends in organism distribution [11]. Several times GIS and mathematical models have been used to solve ecological problems that have a spatial aspect to them [12]. Historical account emphasizes that geographical isolation has been considered a prerequisite for reproductive isolation [8] [13] [14] [15]. Jordan's rule further states that given any species in any region, the nearest related species is not likely to be found in the same region or remote region, but in a neighbouring district separated from the first by a barrier [13] [14] [16]. Recent work has shown that ecological and parapatric speciation is more common than formerly appreciated, and plant species are more sensitive to fine-scale environmental heterogeneity [16] [17] [18] [19]. A report on the closest relatives gives insights into the relative importance of geographical and ecological segregation in speciation. Plants which are characterized as same species are more closely related to each other than to any other species, which can leave a major imprint on the geographical and ecological attributes [20] [21] [22]. The degrees of range overlap and range asymmetry of plant species provide the ability to infer the geographical mode of speciation [16] [23]. Allopatric speciation often times is mistaken for sympatric speciation especially when followed by secondary contact [23] [24] [25] [26]. The greater the reproductive and ecological similarity of plant species to each other than to non-congeners the more recent is the shared ancestry and phylogenetic niche conservatism, as found in a number of plant groups [21] [27] [28]. Nigeria is found in the tropics, where the climate is seasonal and humid. The vegetative zones are controlled by the combined effects of temperature, humidity and the variations that occur in rainfall. This forms a major influence on the

Description of Study Area, Location and Site
Nigeria is a country in West Africa, it has a compact area of 923,768 km 2 , and  Oyo state is located in the Southwest of Nigeria with the capital city as Ibadan and an area cover of 28,454 Km 2 . The state is well drained with rivers flowing from the upland in the North-South direction. The vegetation pattern is that of guinea savannah in the north and that of rain forest in the south. Oyo state is situated between latitude 10˚06'12.048''N and longitude 08˚49'19.507''E. Ogun state is situated between latitude 06˚58'10.11''N and longitude 04˚07'22.92''E, the state covers a landmass of 16,409 Km 2 in the Southwest of Nigeria. The northern part of the state is mainly of derived savannah vegetation, the southern part of mangrove swamp and the central part is of the tropical rain forest belt. Ondo state has a landmass of about 14,788.723 Km 2 in the Southwest geopolitical zone of Nigeria. The geographical coordinates of Ondo lies between latitude 07˚18'38.307''N and longitude 05˚01'37.572''E. The vegetational belt lies within the tropical rain forest zone at the south and sub-savannah forest in the northern fringe. Kwara state is located at the West Central region of Nigeria and is situated in the transitional zone within the forest and the guinea savannah regions of Nigeria. The state is situated within 36,825 Km 2 and found within latitude 09˚17'25.52''N and 03˚51'33.94''E of the equator.
Anambra state is situated in the South East geopolitical zone of Nigeria. The state covers an area of 4416 Km 2 and has tropical rain forest vegetation. The state is located at latitude 05˚51'14''N and longitude 06˚51'36''E of the equator. Ihiala is amongst the local government area of Anambra state. Enugu state is found in the Southeastern region of Nigeria. It lies within the foot of an encarpment which is located in the Cross River basin, its vegetational belt cuts across the tropical rain forest zone with a derived savannah. The geographical coordinates is within latitude 06˚26'40.80''N and longitude 07˚33'51.20''E of the equator. Enugu east is part of its local government area. Ebonyi state is situated in the South east geopolitical zone of Nigeria and covers 5935 Km 2 . It has large deposit F. O. Awala et al.
of salt water and luxuriant vegetation with high rain forest zones in the South and sub-savannah forest in the Northern fringe. The state is found within latitude 06˚14'43.98''N and longitude 08˚10'27.49''E having Afikpo North amongst the Local government area.
Cross Rivers state is a coastal state in the Niger Delta region, it is located in the Southsouth geopolitical zone of Nigeria and occupies 20,156 Km 2 and a geographic coordinates of latitude 06˚36'40.78''N and longitude 08˚47'54.55''E. The vegetation ranges from mangrove swamps through tropical rain forest, to derive savannah, and montane parkland. Ogoja is one of the local government found in Cross River. Akwa Ibom state occupies a total landmass of 8412 Km 2 in the South-south geopolitical zone. It has Tropical rain forest Zone and Fresh water swamp vegetation, it is located within latitude 5˚2'54.89''N and longitude 08˚2'07.27''E. The local government within Akwa Ibom includes amongst others IkotEkpene, MkpatEnin, and Uruan. Bayelsa state in South-south of Nigeria has a landmass of 21,110 Km 2 . The vegetational cover is predominantly fresh water swamp, other ecological zones include: Coastal barrier, Island forest and Mangrove forest. It is located within latitude 05˚10'22.67''N and longitude 07˚41'19.80''E, having Ogbia as one of the local government. Rivers state is located in the Niger Delta region, in the South-south geopolitical zone of Nigeria. It consist of a total landmass of 11,077 Km 2 with a geographic coordinates within 04˚43'57.61''N and longitude 07˚14'54.98''E. The local government areas includes: Tai, Eleme, Etcheamogst others. The vegetation cover towards the Inland part consist of tropical rain forest and the coast many mangrove swamps. The topography of the state ranges from flat plains to the network of rivers to tributaries.

Phytogeographical Field Sampling Design
The spatial distribution of Lagenaria siceraria and locations are some of the major aspects analysed. The species were observed and collected from parts of Rivers state, Akwa Ibom, Cross River, Bayelsa, Anambra, Enugu, Ebonyi, Oyo, Ogun, Ondo, Taraba, Kwara, Plateau, Kano and Kaduna states of Nigeria. The area under study were chosen for the reason of accessibility, availability, and prevalence of the species. A systematic ramdom sampling basesd on simple ecological procedure was carried out with various sampling points of different geographical precision coordinates noted in parts of the states under consideration [4].

Phytogeographical Sampling Procedure
The study involved extensive field trips to different states and herbaria in Nigeria. The geographical and distributional studies of Lagenaria siceraria (Mol.) Standl. were carried out using the herbarium specimen from Forestry herbarium Ibadan, University of Port Harcourt herbarium, University of Uyo herbarium and field collections. The locality and coordinates were recorded using the google map. The data were further used to generate a distributional map of the species.

Result and Discussion
The result of field collections and herbarium studies are summarized in Table 1     The discontinuity in variation that exists within a single species has been of great concern to taxonomist in the definition of speciation [33] [34] [35]. This discontinuity exists as a result of isolation in nature which aids in establishing and widening the gap between species thereby allowing evolution. According to [33], environmental factors had been of consequential effect in shaping the appearance of a plant, hence the various landraces of Lagenaria siceraria (Mol.) Standl.
The spatial relationship of the species both in present and past (Wickens, 2008) were observed using Geographic Information System (GIS) as represented in Table 1. Lagenaria sicerariaas part of the vegetative cover of Nigeria shows great diversity in fruit shape across the agro-ecological region of Nigeria ( Figure   2). From the foregoing, it is observed that the diversity of fruit shapewithin the found fairly continuously throughout the area of distribution, some have distribution patterns which are interrupted by some areas from which the species is absent and this pattern is seen as disjunct distribution [34] [35]. The disjunction might have arisen from the long-range dispersal of the landraces from one area to another.   landraces across the various ecological zones points to the fact that they are vicariance a term introduced [35]. The vicariants may have arisen from migration across the ecological zones and evolving through divergent evolution. Singh G [33] states that geographical separation of lineages leads to lineage independence and ensuing speciation. The separation of the landraces of L. siceraria across the ecological zones of Nigeria over time resulted to the development and maintenance of gene combinations which controls the morphological, physiological and anatomical characters of the species as seen in the diversity of fruit, seed, and   gene. Another major observation is in the development of reproductive isolation when the twenty-four different fruit shapes randomly selected across the agroecological zones were potted in the ecological centre of the University of Port Harcourt, they were subjected to the same environmental condition such as temperature of 26˚C, rainfall, soil texture, they all germinated and grew together under the same condition thereby eliminating environmental plasticity but maintained their specific fruit shapes hence, are not an ecocline but a topocline, since it is found growing across the geographical regions of Nigeria.

Conclusion
The phytodistributional studies of L. siceraria have shown that the landraces have a wide distribution and variation which spreads across the agro-ecological zones ranging from Guinea savannah as the centre of origin having a total of twenty-four different fruit shapes to Tropical rain forest, across the Sudan savannah through the Fresh and Saltwater swamp hence proven to be a topocline