Haven’t gotten out lately, went to Flag with the Sky Island people to put in springs data, going to the Whetstone Mts. this Friday for the first weekend camp out of the year. Supposed to be 91 degrees on Saturday! Hope we go to an elevation with manzanita and hope that there will be some botany or insect people along.
I have previously talked about my discovery of pointleaf manzanita (Arctostaphylos pungens) in bloom on February 2nd in the southern Santa Rita Mts, and my subsequent discoveries on nectar robbery by bees and flies, about the possible hole cutting by thrips, and about the biogeography of the genus. In this paper I plan to talk more about the phylogeny and life history of the genus and how this can perhaps help in understanding the plants relationships with its associates.
The current story is that the subfamliy of Ericaceae, Arbutoideae arose in what is now California some 168 million years ago and spread into a circumpolar region of Mediterranean climate. At around 26 million years ago, the Atlantic Ocean separated different into North American and European/Asian groups (Hileman, Vasey, Parker, 2010).. About 5 million years ago the North American species of the genus Arctostaphylos radiated into the variety we know today This speciation took place mostly through hybridization and polypoidy (whole genome duplication). At base Arctostaphylos has 13 chromosomes while there are species with 26 and 52 and 78 chromosomes. These radiated Arctostaphylos species are edaphic (soil) specialists, they are associated with mycorrhizal and endorphic fungi in the roots and leaves, and there are two types of reproductive strategies that are related to fire and perhaps drought; an obligate seeding mode where fire destroyed plants restart from a seed bank and a facultative sprouting mode where the plant has an underground burl that resprouts after the top part has been burned. About 2/3rds of Arctostaphylos species use obligate seeding (Wahlert, 2005).
(Wahlert, 2005) have created the most current phylogeny of the genus. Molecular data is needed as finding the taxonomy of the genus has not been successful using characters. The philogeny did split the genus into two groups which correspond to a splitting of the genus based on flavinoid profiles (Denford, 1981). It is interesting that A. pungens in California and A. pungens in Arizona fall into two different groups, suggesting that they may be separate species. Of the 98 ingroup assensions tested of which 83 were unique taxa, 44 had the same nrITS (Nuclear Ribosomal Internal Transcribed Spacer) region, while 17 had multiple hits suggesting polyploidy or hybridization. 4 of these were hybrids. So, a little over 1/2 of the tested species were resolved, a big bunch can only be grouped together. Fortunately A. pungens (AZ) and A. pringlei pringlei were resolved as a distinct clade with A. australis. The authors admit that the present technology only loosely resolves the phylogeny but this is still a step forward (Wahlert, 2005).
Obligate seeding and facultative sprouting are two reproductive strategies used in dealing with fire. Sprouting occurs in some 25% of the species but it doesn’t look like it follows the phylogeny and there is evidence of both forms of reproduction within a species (Keeley, Vasey, Parker, 2007). It was hypothesized that facultative sprouting would result in changes in the seed bank and floral abundance because why have flowers if the plant is using a reproductive strategy that doesn’t use them. Tests of this have been very mixed with success or failure mainly depending on what two species are being tested (Kelly, Parker, 1990)(Fulton, Carpenter, 1979)(Fulton, Carpenter, 1979). In Arizona, these species are in a mozaic environment, fire and/or drought can occur on one slope and not another. Whether the plants are on the north side of a mountain or the south side makes a difference. Plant communities around Tucson start at a lower elevation than the Mogollon Rim because of more rain in Tucson, although it is warmer in southern Arizona (Larry Stevens, personal com.). To fully understand this, patterns of variation need to be understood between species, between populations, and within populations.