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Reproduction of the Regal Horned Lizard (Phrynosoma solare) in Captivity

By

Mark A. Brock


INTRODUCTION

Phrynosoma solare have been observed to reproduce in captivity. P. solare are relatively sedentary within the horned lizard groups (Baharav 1975). Their natural diet is known to be over 90% ants during most of their active season, although they may take quantities of other insects when there is abundance. Baharav, in his study noted a diet of 100% ants of the Pogonomyrmex rugosus species. Years of field observation has shown that all observed P. solare populations were coexisting with significant populations of harvester ants of the Pogonomyrmex genus, usually P. rugosus or P. barbatus. In captive populations it has been noted that P. solare are able to take these larger ants as food items at as little as 4 weeks of age, unlike other horned lizards species, who must rely on smaller ants in the hatchling stage (Chew 2002). These factors combine to produce exceptional growth in Phrynosoma solare in their first year. It has been noted by the author that among various P. rugosus nests there will be individuals or nests with significantly smaller ants than those of possibly older or better established nests.

In early April 2004 I received 4 small hatchlings from Joseph Collet from his captive breeding project. These hatchlings were born in September 2003 and labeled as follows:

1. male "J"

2. male "15"

3. female "D"

4. female "21"

The hatchling labeled as "15" was lost in the first week due to an enclosure accident. See photos of two of the remaining subjects in Fig 1. These hatchlings were provided suitable indoor and eventually outdoor habitat, with food items completely consistent with their natural diet. Weight was measured and recorded periodically during the months prior to reproduction. This study was performed to measure the growth progress of captive born hatchling P. solare in captivity. Is it possible that P. solare are able to achieve a body size and maturity significant enough to allow reproduction in less than 12 months from birth?


Fig. 1 Male and Female Phrynosoma solare Hatchlings 10 Apr 2004


METHODS AND MATERIALS

HABITAT
An indoor enclosure was configured in a 15" by 35" terrarium with a substrate of 3 inches of fine beach-like sand purchased from a reptile supply. Lighting consisted of a 160 watt PowerSun UV spectrum flood light by ZooMed. Light duration over the time of indoor habitation varied from 10 to 12 hours per day over the 4 month period they were housed indoors. All three individuals were place in an 8 foot by 8 foot outdoor enclosure on approximately July 1, 2004 where they remained until my relocation to Arizona on August 12th, 2004. This cage was located in Lancaster, California in the eastern most portion of the Mojave Desert. The area was a residential housing track adjacent to a natural desert area where ants were collected. The enclosure was a wire covered wood frame set in the natural substrata and vegetation of the Mojave Desert. This enclosure was wired framed on all sides, but the top was covered with a slightly light permeable shade cloth common to patio roofing.
DIET
The diet provided to these P. solare hatchlings was consistently 99+ % ants of the P. rugosus species for the duration of this record. Pogonomyrmex rugosus are native to most of the natural range of P. solare. The only variation would be the type of ants supplied with a small percentage of P. subnitidus or P. californicus being included at sporadic times during this first year in captivity. There would likely have been some incidental inclusion of wild insects during the period the lizards occupied the outdoor enclosure. No crickets or meal worms were fed to these individuals. Water was offered sporadically via a light spray from a garden hose. Frequency of watering was less than once per weak.

OBSERVATIONS

The P. solare hatchlings adjusted very well to both indoor and outdoor enclosures. No signs of stress due to human presence were noted. In fact, the solare would eat ants while being held in the palm of the author's hand. This calm nature is attributed to being socialized to humans from birth. Because the hatchlings were restricted to an 8 foot by 8 foot enclosure, they did not need to expend significant energy in their quest for either food or looking for a mate. The reduced energy requirement may have contributed to some extent to the rapid growth rate recorded. It should be noted however that P. solare hatchlings observed in the wild maintained similar growth rates. Also of note, P. cornutum under the same captive care parameters did not reach the level of maturity that the P. solare did for the same time period. The P. cornutum required a two year period to reach adult size, and three years to reach breeding maturity. As the hatchlings grew, their larger size enabled them to increase their ant intake significantly. This increased food intake translated into a much faster growth. Weight for these hatchlings was tracked over the first year period as illustrated in Table 1. Growth trends are charted in Table 2.


Phrynosoma solare Hatchling Weight Table 1
Table 1: Weight Tracking


Phrynosoma solare Growth Trending Table 2
Table 2: Growth Trending for Male and Female ("J" and "21")


RESULTS

On 6 August 2004 the captive born female noted above as "21" was found under a small rock with a group of ten eggs. Following are my log notes for that event:

"Large female solare (captive bred from Joe Collet) laid 10 eggs today. They were laid in a dug out area of sand under a rock. The rock was about 6 to 8 inches thick, 15 inches wide and about 20 inches long. She was very obese prior to the event and now is noticeably thinner. Eggs were large and plump, approximately 1 inch in length and .5 inches across. They were pinkish, but were covered with sand by the time I was able to remove them from the enclosure. Approximate time eggs were deposited 4:00 pm 6 Aug 2004. Weight of female after laying eggs is 23.7 grams.


Phrynosoma solare eggs hatching 23 Sep 2004
Fig. 2 Clutch of 10 Phrynosoma solare eggs laid on 06 Aug 2004


These eggs were immediately removed from the enclosure and placed in an incubator in a small dish of vermiculite and water. The temperature was set at 84F. Six of the eggs subsequently hatched from 23 Sep 04 through 3 Oct 04. One of the hatchlings died after his first day for unknown reasons. All others eat and continue to do very well.



Fig. 3 Phrynosoma solare eggs hatching 23 Sep 2004


DISCUSSION

This study does show conclusively that P. solare are able to reproduce at less than 12 months of age. Because the eggs in the wild naturally hatch out in late August thru October, the time period is conducive to potential breeding in the wild before reaching 12 months of age. This information could have significant impact on conservation factors affecting P. solare and could be an important fact affecting further ecological study of the species.


LITERATURE CITED

Baharav, D. 1975 Movement of the Horned Lizard Phrynosoma solare. Copiea 1975. 649-657

Chew. Robert M 2002. THE FOOD HABITS OF THE SYMPATRIC HORNED LIZARDS, Phrynosoma modestum and P. cornutum Publication: larrea-plot.com



Date submitted 23 Jan 2008






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