Arizona Road Trip Jan-Feb 2017 Part 5
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Arizona Road Trip Jan-Feb 2017 Part 5
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Ant Images (1)

The Genus Pheidole (Big-Headed Ants)

Professor E.O. Wilson has written an entire book about Pheidole ants of the New World. The book includes 624 species, with an estimated 1500 species worldwide! The genus is so large that it has been subdivided into Groups. I must admit that I am only confident identifying a few of these species. Most of the species I have observed in the Sonoran Desert region (California & Arizona) belong to the Pilifera Group. Minor workers are only about 2.0 mm long. Major workers are much larger with very large heads compared with their body size--hence, the name "big-headed ants." The nests of some species have majors and "supermajors" with even larger heads, The largest major head I ever found was at Dos Palmas Oasis north of the Salton Sea. Since I had to reconstruct the head from exoskeleton parts from the nest, it may not be completely accurate.

  See Supermajor (Pheidole tepicana) Photographed By Alex Wild  

Since I could not find any intact majors, I attempted to reassemble (using Photoshop) the head from exoskeleton parts recovered from the nest. Assuming these are from the true major caste for this species, the image shows an enormous difference in the head sizes for major and minor workers. have also found Pheidole species on the island of Maui (P. megacephala) and on Owens Peak (P. vistana), the local hill where I hike near my home in San Marcos, CA.

  Pheidole Species On Wayne's Word Ant Genera Page  

Dateland, Arizona

Devil's claw plant (Proboscidea althaeifolia) in full bloom.

Big-Headed Ants (Pheidole) In Borrego Springs

In our southwest desert, tiny Pheidole ants have major workers to defend their nest against army ant raids. The major worker has an enormous head in proportion to its body. Some species actually block the nest entrance with their heads!

Big-Headed Ants (Pheidole) Near Willcox, Arizona

The heads of major workers are quite reddish. The minor wokers are only 2 mm in length, compared with a local San Marcos species (P. vistana) with minor workers up to 4.0 mm long.

Big-Headed Ants In The Superstition Mtns

This may be the same species found near Willcox, Arizona.

Riparian Preserve At Gilbert Water Ranch

Another Pheidole In The Superstitions

Gently holding a major worker who was not happy. Both majors and minors were reddish-brown (with darker gaster) and larger than previous Pheidole found in Superstitions. Previous collection had tiny black workers 2 mm long. When I first encountered their nest I thought they were fire ants (Solenopsis); however, they have a 3-segmented antennal club and do not sting. They also give off an odor I have previously detected in Pheidole. This species appears to be in the Fallax Group, along wth P. vistana on Owens Peak and Daley Ranch (San Diego County). It is similar to P. desertorum.

This species appears to be in the Fallax Group, along wth P. vistana on Owens Peak and Daley Ranch (San Diego County). In fact, the minors have a very long scape and elongated head like P. vistana. It is similar to P. desertorum. GPS coordinates taken with iPhone: N. 33.39447, W. 111.50935.

Pheidole At Lower Salt River

This appears to be the same species as in previous image from the Superstitions. Both majors and minors were reddish-brown (with darker gaster) and larger than previous Pheidole. As in the previous image, when I first encountered their swarming nest under a rock I thought they were fire ants (Solenopsis); however, they had a 3-segmented antennal club and did not sting. They also gave off an odor I have previously detected in Pheidole. This species appears to be in the Fallax Group, along wth P. vistana on Owens Peak and Daley Ranch (San Diego County). It is similar to P. desertorum.

Epigenetics: The Making of Ant Castes

New research on ants and honeybees points to DNA methylation as a crucial factor in determining the caste of a developing individual. Epigenetics refers to developmental changes in gene expression or phenotype without changing the original DNA sequence. Epigenetic traits are caused by methylation of certain DNA bases, thus affecting the development of the larva. It is a mechanism that occurs by the addition of a methyl (CH3) group to DNA, thereby often modifying the function of the genes.

Exons In Epigenetic Ant Research

In eukaryotic cells, the initial messenger RNA (M-RNA) transcribed from the DNA (gene) is modified (shortened) before it leaves the nucleus. Sections of the M-RNA strand called introns are removed, and the remaining portions called exons are spliced together to form a shortened (edited) strand of mature M-RNA that leaves the nucleus and travels to the ribosome for translation into protein. Perhaps the deleted sections (introns) were needed by our ancestors, but are no longer necessary. In fact, this hypothesis was actually utilized in an episode of Star Trek: The Next Generation. In this episode the crew was reverting back to their ancestral state because their introns were reactivated.

According to A. Chittka, Y. Wurm and L. Chittka (2012): "As in honeybees, the bulk of DNA methylation in these ants was in the exons of transcribed genes, with the levels of methylation correlating positively with gene expression."

    Epigenetics: The Making of Ant Castes by Alexandra Chittka, Yannick Wurm, Lars Chittka. Current Biology Volume 22, Issue 19, pR835-R838, 9 October 2012.   Full Text Version   PDF Version

  Misrepresentations Of Science: Epigenetics & Power Of The Mind  

DNA is the master molecule of life that contains in coded form all of our genetic characteristics. In fact, the remarkable diversity of life is based on the "infinite" arrangements of DNA molecules. Mutations (stable hereditary changes in DNA) may lead to the evolution of new species. Although DNA sequences (genes) may remain stable for many generations, they may be turned on or off by regulator proteins. In the following simplified illustration of a small section of DNA with 68 base pairs (rungs), the molecule has 4^68 possible arrangements or 87 duodecillion (87 followed by 39 zeros)! [The previous statement assumes an unlimited number of A's, T's, C's and G's.] In epigenetic traits, like the castes of ants, the DNA is methylated but the original base sequence is not altered.

Some species of Pheidole have a supermajor (supersoldier) that is larger than regular majors. It has a strikingly massive head compared with its body. These species have 3 castes: minors, majors and supermajors. Most of the 1000+ species of Pheidole have only 2 castes, but apparently have the genetic potential (ancestral DNA) to produce supersoldiers. Biology professor Ehab Abouheif at McGill University in Montreal discovered that dabbing larvae with methoprene, a chemical that mimics juvenile hormone, will induce the development of supersoldiers. These large biting ants are presumably better able to defend the colony against invasions of aggressive army ants.

Telomeres In Epigenetic Ant Research

Telomeres are repetitive strands of DNA (sequences of repetitive bases) at the terminal ends of linear chromosomes. They play an essential role in maintaining the integrity of the chromosome by protecting it from degradation and from end-to-end fusion with other chromosomes. Telomeres are essentially protective "end caps" of non-coding DNA at the extreme ends of chromosomes. Telomeres have been metaphorically compared with the tips of shoelaces that keep the laces from unraveling. Each time a cell divides, the telomeres lose a small amount of DNA. Eventually, when all of the telomere DNA is gone, the cell can no longer divide and dies. End replication problem is not an issue in prokaryotic cells because they have circular DNA molecules without ends.

  Evolution Page: Telomeres & Aging Process  

Another interesting area of ant research concerns the biology of aging: "The link between caste-specific differential methylation and maintenance of telomeres (chromosome ends) is intriguing because of its potential links to the biology of ageing." Queens and worker ants are diploid with 2 sets of chromosomes and males are haploid with only one set. Queens may live more than 20 years while workers may only live a few months, even though they have the same DNA. How is this possible? Does it involve telomeres?

In the Indian jumping ant (Harpegnathos saltator), special egg-laying workers capable of mating (called gamergates) can replace an aging queen. A study of the genome and expressed genes of gamergates found that the production of enzymes that slow aging (telomerase and sirtuin deacetylases) are increased when workers turn into queens, thus increasing their longevity like queens.

  Antwiki Key To The Pheidole Pilifera Group  
  Antwiki Key To The Pheidole Fallax Group  
  Pheidole vistana in San Diego County