Modelling Malpighian tubule crystals within the predatory soil mite Pergamasus longicornis (Mesostigmata: Parasitidae)

Abstract

The occurrence of refractive crystals (aka guanine) is characterised in the Malpighian tubules of the free-living predatory parasitiform soil mite Pergamasus longicornis (Berlese) from a temporal series of histological sections during and after feeding on larval dipteran prey. The tubular system behaves as a single uniform entity during digestion. Malpighian mechanisms are not the ‘concentrative’ mechanism sought for the early stasis in gut size during the second later phase of prey feeding. Nor are Malpighian changes associated with the time of ‘anal dabbing’ during feeding. Peak gut expansion precedes peak Malpighian tubule guanine crystal occurrence in a hysteretic manner. There is no evidence of Malpighian tubule expansion by fluid alone. Crystals are not found during the slow phase of liquidised prey digestion. Malpighian tubules do not appear to be osmoregulatory. Malpighian guanine is only observed 48 h to 10 days after the commencement of feeding. Post digestion guanine crystal levels in the expanded Malpighian tubules are high—peaking as a pulse 5 days after the start of feeding (i.e. after the gut is void of food at 52.5 h). The half-life of guanine elimination from the tubules is 53 h. Evidence for a physiological input cascade is found—the effective half-life of guanine appearance in the Malpighian tubules being 7.8–16.7 h. Crystals are found present at all times in the lumen of the rectal vesicle and not anywhere else lumenally in the gut at all. No guanine was observed inside gut cells. There is no evidence for the storage in the rectal vesicle of a ‘pulse’ of Malpighian excretory products from a discrete ‘pulse’ of prey ingestion. A latent egestive common catabolic phase in the gut is inferred commencing 12.5 h after the start of feeding which may cause the rectal vesicle to expand due to the catabolism of current or previous meals. Malpighian tubules swell as the gut contracts in size over time post-prandially. There is evidence that at a gross level the contents of the rectal vesicle are mechanically voided by the physical mechanism of overall gut expansion altering the effective idiosomal volume available during prey ingestion. A complete cycle of feeding, digestion, egestion and excretion is approximately 9 days. Hunger/starvation likely commences at 10 days after the start of feeding. Up to 15 days may be needed to completely clear the idiosoma of excretory material. Nomograms for predicting the likely feeding time of mites from observations of idiosomal guanine in field samples indicate that as few as 5–6 mites scoring positive for Malpighian tubule guanine out of 20 infers a high probability that the typical time from start of feeding in a population sample was about 6 days (range 3–8 days) ago.

The gut epithelium from feeding to fasting in the predatory soil mite Pergamasus longicornis (Mesostigmata: Parasitidae): one tissue, two roles

“…Gut cell esterase activity, if present, was patchy and sporadic in discrete local sub-oval 'hot ( d i,j ) between the complete histologically scored character data at each time point from feeding to fasting in Pergamasus longicornis. Uses all cellular data herein plus that from Bowman (2014Bowman ( , 2017a. Distance around circle is reciprocally weighted Jacquard similarity index between adjacent sequentially displayed points, confirming four phases.…”

“…Haemoglobin digestion (O'Hagan 1974) and the accumulation of secretions within gut cells occurs, followed by the shedding of the latter cells or haematin itself into the lumen throughout all of the mid gut. The temporal pattern of guanine in the Malpighian tubules of this species is approximately 180 • out of phase with feeding just like laelaptids (Zamsky 1964) and like in pergamasids (Bowman 2017a).…”

“…At each of the i = 34 time points, the histological (but not the histochemical) data herein plus those of Bowman (2014Bowman ( , 2017a were combined. The resultant k = 785 characters (covering gut and Malpighian tubule, lumenal and cellular states-initially scored 0, 1, or 2) were rescaled (to a 0 to 1 probability range) to yield a matrix , such that the elements A i,k were the kth normalised state for the ith time point.…”

“…(c) Check for a 'digestive switch' around 2 h and an 'egestive' switch around 4 h (Bowman 2014, 2017b), (d) Recheck if food elimination is slower in the anterior gut compared to the posterior parts (i.e., the antithesis of hypothesis (iv) in Bowman 2017b), (e) Check if cellular processes are 'stiff', and how stiff they are compared to gut expansion/ contraction (Bowman 2014), Malpighian processes (Bowman 2017a), and lumenal content processing (Bowman 2017b), (f) Check 'hypothesis (viii)' from Bowman (2017b) as to just what is a good indicator of starvation in this arachnid, via a critical assessment of all cell types and their vacuolation quantitatively over time. These will be denoted as 'Check (a)' through to 'Check (f)' in the "Discussion"for easy cross reference.…”

“…cases also used data from Bowman (2014Bowman ( , 2017a to provide insight in teasing out possible cellular functions. Vacuolation over all cell types was summarised and kinetically modelled in a similar fashion.…”