Abstract
Abstract. The study of the morphology of living organisms is essential to understand their evolution and diversity. This study aims to determine the importance of climatic gradients in the diversity of pollen morphotypes using Atriplex halimus L. (Amaranthaceae) as a model species. Atriplex halimus is a perennial shrubby plant, polymorphic and very resistant to severe environmental conditions. In seven bioclimatic zones, ranging from mesic conditions in the north to hot–hyperarid in the south, pollen samples were collected from 49 sites, with seven accessions per bioclimate. Under a light microscope, pollen grains were selected and analyzed from three anthers of different flowers. Besides the usual pollen grain types, some previously unknown morphotypes, such as sulcate, triangular, and ovoid, were observed and described at the different climatic zones. A total of 10 pollen grain shapes were quantified and discussed following their specific occurrences within different climatic zones. Occurrence frequencies of different pollen shapes ranged between 0 % and 85.7 %, where the pantoporate spheroidal was the most widespread in all climatic zones, especially in the desert climate (85.7 %). Five pollen types occurred exclusively once per climate zone. The pantoporate prolate spheroidal in mesomediterranean climate with a long dry season (28.6 %), sulcate in the xerothermomediterranean climate (14.3%), pantoporate subtriangular in the subdesert climate with a short dry season (14.3 %), and pantoporate subprolate and boat-shaped in a subdesert climate with a long dry season with 14.3 % for each. Our findings help to understand the evolutionary effects of climate gradients on pollen morphology and variability in arid and desert areas and point towards a high degree of specialization in order to maximize trade-offs between pollination efficiency and protection of pollen grains from dehydration.
Highlights
Pollen grain studies need to cover all phenotypical aspects, polarity traits, and cytoplasmic characteristics in order to efficiently resolve current palynological problems and advance our understanding of the biology of pollination (Muller, 1979; Prieu, 2015)
Results of generalized linear model (GLM) testing the variation in pollen shape occurrences among the bioclimatic zones showed that there was no significant difference in occurrence odds of all pollen aspects except for the pantoaperturate spheroidal type whose occurrences varied significantly between climatic regions (χ 2 = 14.39, p = 0.026) (Table 2)
The generalized linear mixed-effect model (GLMM) testing effects of latitude, longitude, and altitude on the spatial occurrence of each pollen grain shape revealed that latitude had a negative effect on occurrence odds of all pollen aspects except for the pantoaperturate spheroidal type that was positive (GLMM: t = 1.581, p = 0.122); all these effects were not statistically significant except for the pantoporate triangular pyramid type (t = −2.41, p = 0.021) (Table 3)
Summary
Pollen grain studies need to cover all phenotypical aspects (e.g., apertures, shapes, pores, dimensions, colors), polarity traits, and cytoplasmic characteristics in order to efficiently resolve current palynological problems (species and varietal identification in the fields of botany, paleobotany, and forensic palynology) and advance our understanding of the biology of pollination (Muller, 1979; Prieu, 2015). H. Fatmi et al.: Morphological diversity of Atriplex halimus pollen in Algeria flowers and pollen production per flower. Fatmi et al.: Morphological diversity of Atriplex halimus pollen in Algeria flowers and pollen production per flower These stresses can be related to soil fertility (Lau et al, 1995; Havens et al, 1995), previous production of fruits and seeds (Delph, 1990; Young and Stanton, 1990a; Stephenson et al, 1994), mycorrhizal infection and effectiveness (Lau et al, 1995), and herbivory intensity (Quesada et al, 1995)
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